FWIW, I recently installed a fresh engine, same everything - heads, cam, timing, pistons, etc. as the one it replaced and just swapped the carb over. First pass I thought it was a dog as I lost .03-.04 in 60'. I jetted down 2 #'s and got most of it back with ET's as good as ever. Obviously, despite having the same set-up, the new engine needed less jet and still needs the accellerator pump circuit optimized. So if you went to a completely different engine combo, the carb likely needs recalibrating. The low fuel pressure and big cam is likely aggravating the situation.

My 60's have been as quick as 1.46 and runs as fast as 11.14 @ 117 weighing 3,540 with unported heads and a .474" cam in a 360.