Imo, this a classic case of where substituting a “known good” part would help shed some light of where to look.

My suggestion is to see if maybe one of your racing buddies has a known good working bracket race carb with 4 corner idle you could put on the motor........ run it for a while, get the motor up to operating temp, etc...... then pull it off and see if the manifold is wet like with the other carb or not.

If the plugs aren’t wet, and the manifold looks normal....... you know it’s simply a carb issue, and can stop looking at other items as being where the problem is.

From this side of the keyboard...... I’m betting it’s a carb issue.

My 383, which had a bigger cam than yours, and blocked heat crossover didn’t have a wet manifold plenum, and the same set of plugs were used for well over 100 dyno pulls and probably 200 passes in the car(3 seasons)....... and still looked fine.
Also...... with regards to the blocked heat crossover....... my guess is virtually every good running stocker has a blocked heat crossover(not to mention the countless other race car motors that use “air gap” style manifolds without crossover heat).

Of course, I had a good working carb with low speed calibration suited towards poor carb signal at lower rpms.

I won’t get into a debate over it, but the 2.5pv isn’t what you want.