You could get a 440 in 71... now 72 is a different story. 8 3/4 is a good rear end and will hold up to alot of abuse. Chryslers version of the 9". He seems to be telling the truth, but I do not know how to find out about # matching drivetrains. The 440s and all big blocks use a bigger u joint in their rear ends. Other than that they are the same as a performance small block. ie 340 or 360. That is a nice looking Challenger and in sleeper mode as a rallye.