Advance and transfer slots

The good news that my engine combo is similar to yours, so I can tell you what worked on mine, and it will sortof transfer to yours.
And I am at 930ft, so we're on the same page. and I too have a 4 speed.
My combo;
Eddy-headed 367, with a 276/286/110 cam which is 230/237@050
the Scr is 10.95, the Dcr is 8.6, and the pressure is ~180psi
Unwrapped/uncoated headers. Airgap/Ancient 750DP from circa 1970.
Fresh-Air, and coolant at 207, exactly. This engine, except for One Mile, has never run on anything but 87E10.
My timing events are;
276 intake/115 comp/104 power/286 exst/61overlap/ in@107
Compared to yours at about
286 intake/112 comp/104 power/290 exst/72 overlap/ in@105

Ok Opinions first;
That's a nice cam.
Headers coated inside and out, nice.
I Really hope you're running fresh air to the carb.
I hope your Performer is an AirGap.

Let's look at the problems.....
heat soak at shutdown
very hot underhood environment

My Experience
1) With a properly synced T-Slot, I can run the timing down to 5*, and in gear, she will idle across any hard/level/even parking lot at 550/500 on a good day; as long as I want it to.
2) With a manual trans, if I run the usual 12>14, the engine will start to buck, as the rpm falls.. Carb-wise, I have tried everything to get it to run down there and nothing worked. I reasoned that, the big 750DP just could not meter properly at that low of an rpm. I was wrong. Not until I started taking timing out, did she smooth right out.
IMO, this bucking was caused by too-powerful a burn in the cylinder. By retarding the Idle-timing, Peak cylinder pressure is lower, and it occurs later in the stroke, where the piston is lower in the cylinder. Thus the pressure is lower, and with the piston running away from the expanding gasses, the pressure is also more even. Thus the engine loses Idle-Power, and it smooths right out.. at idle, your engine only needs something like 5 hp, so there is no good reason to idle it at much more; especially not with a manual-trans.
Ok so yes, at 5* some heat goes into the exhaust; but think about it; At 550 rpm versus 850, there are only 65% as many compression/power events per time-period ....... so then; so what if there is more heat per pulse entering the ports; the average over time is still probably less.

And finally, How much time does your engine spend at idle?

Mine, in city driving, spends a lot of time maybe not exactly at idle, but at close to it, cuz I run 3.55s. I spent a lotta time getting my engine to run rock-steady at 207 degrees. Part of that was the Airgap, but the bigger difference came when I cut a hole in my hood, installed a nice Mr.Gaskett oval air-filter housing on top of the hood, and boxed/sealed the airhorn to the underside of the hood.
These changes, allowed me to lean out the carb some more at idle, and together, the heating issues disappeared for good.
My normal timing is 12/14, cuz this allows me to punch it, from idling in gear, no slipping the clutch.
I have a dash-mounted, adjustable, electronic timing module, with a range of 15*, that allows me to change the timing, on the fly, right from the driver's seat.
My Timing curve is:
12>14 at Idle, going to 28*@2800, going to 32/34@~3400. This allows me to run 87E10 with out detonation.
The ported VA has been modified to bring in up to 22* at 15inches
The Timing module is usually set to be able to add 6* or subtract 9*.
At 2800=64mph, the Cruise-timing is 28 plus 22 plus 6*, equals 56.
But I have a GVod, so the Cruise-rpm is closer to 65=2240, which is ~4* less.
To deal with the 500rpm Idle, I have installed a Hi-volume oilpump and a 7qt pan. With my Commando 3.09 Low, 500rpm is 3.6mph; so parading is on the table.

I should tell you;
That when I first assembled this engine in 1999, with a 292/292/108 cam, that first summer was very tense. That combo ran hot no matter what I did, and every time I shut it off, I had to wait 20 minutes before it would crank.
I finally tore the engine down and increased both the skirt clearance, and the ring gaps, which together with all the previous changes, solved it for good.

Summary.
Ok so, one more time, how much time does your engine spend at idle?
To recap the changes that I made;
I loosened up the engine, and
I fixed the cooling system, and
I elevated the intake up off the hot valley oil, and
I sent fresh cold air into the carb, and
I installed that big road-race oil pan, looking for a lil more radiating area.
I increased oiling onto my valvesprings to try and keep them cool. This required a lil ingenuity to get the oil back into the pan in a timely manner.
I divorced the one-piece 3/8ths pump to carb fuel line from the engine.
As to the cooling system;
8-vane pump with the anti-cavitation plate, 195 hi-flow stat, 7-blade all-steel A/C fan on a big Ford Thermostatic clutch, in a shroud, recirculating type expansion tank, and a restricted bypass hose. The rad is still the factory 1973 rad off a 318 Swinger with A/C, installed into the six-cylinder rad support. It's so ancient that even the patches on it have patches. and after the thing ran a rock-solid 207*F, I installed a 7pound cap.
After that;
I painted my Eddys, Three coats of heavy paint, to try and keep some heat in them, lol
BTW
IMO,
for a manual-tran streeter; forget trying to tune that beast with a vacuum gauge. That method will lead you down a long path of frustration. WHO the heck cares what the Idle-vacuum is. Let it be what it will be.
The lower the better, cuz it will prevent the dreaded bucking. My 292/108cam ran down at under 10, like 8inches IIRC.

Conclusion
This is how my car is set up. I'm not telling you this is how yours should be. I am reasonably confident that your combo, which I'm guessing it has iron heads, no quench, and not enough cylinder pressure, so it's gonna respond a lil different. So then, just pick and choose some of these tips, as many as it takes, until you get your heat under control.
I very highly recommend that you not try to run automatic-trans type of Idle-timing. Keep it conservative in the 10>14 range, which will get your Transfer Slots close to correct, at 750 rpm.

If you can't run down at 750 or less;
I'll take a wild guess that the engine has excessive internal friction.... like mine did, OR
the engine is getting air from some unauthorized place, OR
the oil is getting up into the crank. Nothing steals Idle-power like windage.
As has been mentioned,
as the manifold vacuum gets weaker, the PCV may not function correctly. I have a box of those I collected over the years. The PCV at idle has a fixed orifice, that cannot be closed. This is not so important to know with a 4-corner idle, cuz you can get air from the secondaries, and just put some fuel in it. If you try that with a standard carb, the dry air back there will cause AFR issues.
So, but it is important to know for guys running a cam about your size or bigger, using a standard carb. It will have to get bypass air from somewhere else. For a while, I ran two PCVs, which actually worked pretty good. But in the end, I just drilled small holes thru my Primary valves.
However, if the PCV will not stay "closed" at idle, now you have tuning problem. Just pull it out of the running engine; and look, or pinch it shut at idle. If you can't get the rpm down, this is the place to look first, but IMO, I don't think your cam will do that; But it will want at least some bypass air; my guess is the equivalent of one hole of 3/32inch, in each primary blade, in the general vicinity of the idle discharge ports but not too close to the edge. With your 4-corner idle, you should be able to just crack the secondaries. But again, cracking the secondaries, with fuel, will cause the Idle rpm to go up. Thus you will be tempted to close the curb-idle screw ....... which will change the Transfer-Slot exposure, which, when it closes too far, will get you an off-idle stumble, and/or a hesitation. The solution is to leave the slot exposure high enough to not get the stumble, and instead, just retard the stinking Idle timing.
If the Idle-timing gets down to say 8*, my guess is you are interpreting something wrongly. If you drilled holes, my guess is that they are too big, lol.
Oh finally
IMO, trying to solve a heatsoak issue with ignition timing is gonna be very frustrating. In the end, you're gonna have to figure out how to keep the carb cool, and cool fuel helps.
When you shut the engine off, the heat will come up and everything gets hot. NOTHING will stop it from eventually boiling at least some of the gas away.
Gasoline is made up of several different molecules most of which have different boiling points. The lightest ones might boil at 95*F, the heavier at up to 400. Just try lighting that off!
BTW, ethanol boils at 173*F so all those guys who blame boiling ethanol for their woes, I'm gonna suggest are probably wrong. Like I said earlier, my 430hp 367 has never run anything but "gasohol" except for 1/2 mile, which was 4 Eighth-Mile runs.

Ok I got some errands to run, and I just know, somebody is gonna start something. Just remember, this is what worked for me and your results may vary, lol.

I might do some editing later, but right now, I gotta run.
Ok all done