Geoff,
The guy that built my car said that at the time he built it he was told that the Ford 2.8L V6 was the biggest engine that would fit in the front engine version of the FiberFab design. The Ford V6 fits only because it is a 60 degree configuration vs the typical 90 degree on most V6s and V8s. That makes this engine much narrower. So, you could measure but I think the 302 might be pushing out the sides of the MG.
I hope I’m right about the tranny too. Not being able to get it into gear most certainly sounds like a “linkage” problem.
Best of Luck!
Rich