That's an 8-1/4 not a 9-1/4 rear.
The only real difference in a 63 engine besides a cast crank vs the original 82 engine's cast crank. The head is slightly different but the important part (combustion chamber design) is largely the same
I just overhauled a 74/6 to put in my 85, is did the oversized valves and shaved the head and block, converted to the 2 bbl, and had oregtcams grind me an 819. I'm not driving it yet, I'm slowly doing bodywork now.