All I can tell you is my formula s 65 cuda has a 318 it fits like a glove! No issues what so ever. I would tell you the issues for the early a body car is the engine area is small block only! I do know some guys make motor mounts that allow the motor to sit up a little bit, this then makes the issue of the hood and air cleaner fit. I have no issues with mine, it is my second barracuda a body with a 318. Runs good the first one ran high 12's at the 1/4 mile, this one not quite so quick yet! One will run into issue if you try to go with headers as there is minimal space, I have dual exhaust off the stock exhaust.
65Cudalover