For what it’s worth, I have had a very similar issue with a 318 + .040 overvbore, XE268, SA 670 carb, 3.23s, and 2500 stall TC, all in an A body. Initial timing was/is at 18 degrees, total at about 37 degrees, all in by 2400. Car had big idle speed drop when put into drive and zero guts on the low end or from a stop. Turns out the converter’s insides had come apart. One new TC later, it easily will roast the tires from a light brake stand and break loose from a hard launch at a dead stop. Pulls hard for a small motor.

Currently, I run 69 jets in the primaries and 73s in the secondaries, with a fairly light secondary spring. The stock settings were a little lean on cruise.