750 Holley or 650 Holley DP carb for 340-4 speed?

And I agree, for track work, more gear. Depending on your cam/redline, the 3.55s might get you to the finish line with just 3 gears or a possible shift just before the line. Not the best for ETs.If you want to ET well you will need all 4 gears, and be lightning fast on the shifts. A 4.10/4.30 will get you close, but DO THE MATH.
-AS an aside, Jim, I hear you on the screaming intake. I remember the TQs. That part throttle-moan at secondary tip-in is unmistakeable. I loved the sound of my L/C 360 TQ trying to pull through the A/T and 2.76s from 2200rpm, in my 71 Monaco.I could never find it in my H/C 360M/T, S-clone. It just built rpm too fast.