i think you are right about the carb.however,there was a 428 super stock mustang that went 9.50s with the factory style carb.it might do better in stock class.many years ago dick serdinak ran nhra stock with his full weight boss 429 car,and went 10.70s with it.not a max effort like todays cars for sure.but then again,how much cfm can an engine really need for that? 1250 dominator on kaase intake would be killer!
i also have a boss 429 block i just posted here for sale if hes intrested.