Trying to figure out the wheel size I need to order.

I had to upgrade to an 8 3/4 rearend (drag racing) and found one set-up for a Dart. Problem is, it appears that it's actually a B body rearend with A body perches...

I don't want to have it cut down if I can avoid. I have a '65 Barracuda, looking for 15 x 7 but can't figure out the offset and back spacing I need to clear the fenders.

Any help or guidance would be greatly appreciate.