Engine Dieseling - Options?

There is only one cause of Run-on, after shutdown; and that is, that the engine,
by it's speed of rotation,
is able to pull fuel and air in, in about the correct ratio, that either ;
the heat of compression is able to cause it to combust, or
the chamber has hot-spots in it that light the fuel off, like a glow-plug.
If you remove one of the three/four, your troubles are over.

The heat of compression is already built into the engine, and cannot easily be changed. Hot-spots well you mighta missed something.
Of course the easiest to do is to close the throttle.
But if your timing is already way too much, then it won't idle.

So here is my tune from when I was running a 292/292/108 in my 11.3Scr 360. The 292 is advertised as [email protected] IIRC. See note 1

Note 1
Back the IDLE-timing up, to 16*. This will force you to open the curb idle screw.
Put the mixture screws to 7/8 turn. This will force you to open the throttle some more
Make sure the PCV is correctly plumbed and working.
Defeat the Vacuum advance for this test.
If your DP carb does NOT have a 4-corner idle, make sure the secondaries are closed up tight but not sticking, both sides the same.
If your DP carb does have a 4-corner idle; IDK what to do with those on this size cam; I didn't need it.
Start the car and warm the engine up. If it doesn't want to stay running, just crank in the speed screw.
After it is warmed up, reduce the Idle speed to 800ish.
That was my base tune.

If it runs like crap and you are 100% satisfied that the lifters are lashed right, and you have NO vacuum leaks anywhere, including inside the crankcase, the brake booster, and the PCV circuit; AND
the fuel is fresh, the level is correct and stable, AND
the plugs are clean, not compromised, and the gaps are not Too Tight.
Then
Put a shop rag in the secondaries. The rpm should nor change much if at all. The secondaries must NOT be pulling DRY air. If it does, the back cylinders will run lean.....making the engine run like crap and the exhaust will burn your eyes. Fix it.
Next,
Begin covering the primaries.
If the rpm goes up, your primaries are lean
If the rpm goes down, your primaries are already rich.
Fix this and your problems will be gone. see note 4
Before you begin, look for a tip-in hesitation. see note 2
After you finalize your Idle-timing, you will have to revisit your max power-timing, your rate and shape of the advance curve, and finally, start tuning the Vcan.

Note 2
The tip-in hesitation is unrelated to the accelerator pump. You just very slowly,gently tip the throttle in. If the rpm hesitates, that's gonna be PITA forever; you gotta get rid of it.
The tip in hesitation indicates that your throttle is too far closed and the transfers are too slow to get moving, crank up the idlespeed 1/2 turn and try again. Repeat as may be necessary, to get rid of the tip-in hesitation.
You can fudge the mixture screws but when finished, at the end of the tune, they should be at about 3/4 turn,+/- ,1/8 turn.If the rpm climbs past 850, retard the timing.
When you end up idling on the transfers and the mixture screws centered in their adjustment range, this is IDK, 70/80% of the battle.
When you get to this point; Do not change the curb-idle screw setting! Leave it where it is! if you change it, your tip-in hesitation will come back. If you need to change your idle speed, you will have to figure out a different way to do it. see note 3

Note 3
Your other choices for setting the idle speed are; timing and idle-air bypass; mostly timing; and changing the fuel level or the IABs, or the IFRs. If you get to thinking about IABs and IFRs I'm not your guy. I have never had to mess with those.

Note 4
My 292 cam wanted more air. I drilled holes in the throttle blades, one in each valve, on the front sides between the transfer slots and mixture screws, about a quarter inch back from the front edges. I started with 1/16 each and ended at 1/8" each, but 1/8 holes were too big. So I had to solder them up, move over, and start over.
Maintain your idle speed after each drilling. and retest with the shoprag. I doubt you will get completely rid of the rich running with drilling the holes (Idle-air bypass), So I suggest you stop at 3/32, and drive it for a while. Note; adding air in this way will increase your idle speed! so take it easy on the holes.
The whole purpose of doing this is so you can leave the throttles in the correct position up on the transfer-slots, to prevent the PITA idle tip-in hesitation, and to provide the correct AFR for the slow-speed circuit.
If you crank in the timing: your engine will pick up power, and you will be able to cruise down there on less throttle, and so the engine will be lean all the time in that zone. If you drive too slow, the engine will pull air around the throttle valves thru the T-slots, but the T-slots will go lean. Then your spark plugs will get hot. And then,when you stomp on it, it all goes to crap. IMO, there is no good reason to run a lot of timing at idle. With an automatic, there is no good reason even to run a lot of timing below stall. If you think you need more timing down there, put it into the rate of advance, or into the V-can system.Your engine will thank you for it. Anyway, that's my two cents.....
Think about it;
At idle...... the engine is at idle! it only needs enough power to idle, and to not stall when you put it into gear. My 292 cam idled at 600 in first gear/A833 at 5* advance, pulling itself thru the parking lot. This is my proof that your engine doesn't need mega idle-timing.
If you put it into gear and stomp on it, the Rs fly up to stall speed and the engine doesn't care what the timing was anywhere below stall.
The only time the engine cares about the timing between idle and stall, is at Part throttle..... and that is where your Vcan comes into play. So instead of trying to force an arbitrary timing number on your tune; let the engine tell you what idle-timing it wants. If she tells you 16/14 or 12, or whatever, is enough, listen to her. Your idle-timing is only not enough when the engine stalls going into gear,lol.