Need Quick Fuel carb tuning assistance

What I would do;
Reset the fuel level slightly lower, make sure the slosh-tubes are installed on the bowl-vents,and replace the 6.5 PV with a 10.5, and downjet the primaries to 68s, and
install whatever sparkplug fits your heads that matches the RN12YCs, in heat range. Those plugs IMO are fantastic; mine have over 100,000 miles on them, fired by the Big Yellow Accell square top. .
And I would work my way up to 200*F minimum coolant temp.
My idle timing is just 14*, on purpose, (different story) and I don't have an A/F gauge on my engine, (also different story). My distributor has a two-stage curve in it. It begins advancing at 900/1000 and is all in at 3400. The kink is at 2800, where the timing is 28*, all with the initial of 14*. And the Vcan ( you gotta have a Vcan with a manual trans and a 230* or less cam), is modded to provide 22*, and I bring it in as fast as it is able (aluminum heads).

I had a 340ish hp 367 with a manual trans and 3.55s. At 930ft elevation, it would initiate a second gear spin at up to 55mph with 275BFGs.
245s were a dangerous tire for me, as the car would spin out on every turn with just a tad too much throttle (ancient 750DP). I often found myself up on the median and facing backwards. The thing about manual trans cars is that the engine is directly married to the tires, and an 11/1 Scr engine has a lot of resistance to being turned (compression braking) by the tires, and 245s are just too small. So when I would take my foot off the gas in mid-turn with the steering fast approaching full-lock,( yeah I know; too hot!), the tires would simply give up and become skis, and around I would go, again. It took 295s to make cornering fun again. These tires have enough sideways rubber that by simply towing the clutch, the tires regained traction, and the car would recover. I can drive in traffic again!
Later I swapped out the 223cam for a 230, and traded away a bit of bottom end, to get a top-end rush, like the 292/108 had done.. The loss of torque at the bottom was so severe that I had to regear the back; first 3.91s then 4.30s. This eventually (another story) led to the Commando box with a 3.09 low, and a return of the 3.55s. Now it takes off like as if it had 4.10s, perfect for my combo.

Get your idle and low-speed bugged out first before moving up. The primary throttle has to near close, to get the transfer slot synchronized. Don't be afraid to give up some idle timing. Forget the idle vacuum, IMO, that means nothing........... cuz nobody drives a big-cam manual-trans engine, at idle. Well almost nobody (another story). To make 400hp with an iron headed 340 takes a lotta rpm, and so, a big cam. I'm guessing your engine should be idling at 750/800 at 10 inches or less. If it is higher and you have a 292/509/108 cam or more, then your transfer-slot sync needs work.
FYI;It is possible to drive a 292/108 cammed 367 at 550rpm in gear on flat,level, hard ground, with a nicely T-port synchronized, 50 year old 750DP, on an AG intake, with 5* of lead; oh wait, that's 360 power,lol.
Don't be afraid to take out some idle-timing. IMO you can't, or shouldn't, or I don't recommend it, run the same idle-timing on a hi-compression M/T car, that might be "normal" for an automatic; and it's no big deal to run 14ish in your combo. You can hide a lotta crap carb and distributor adjustments with a fluid coupling stalling at 2400 or more. But a combo like yours with 3.55s or less, has to be pretty close to perfect, else you will be riding the clutch all the time, at low mphs.
Happy HotRodding