1969 Dodge Dart GT “driver” build

So you've converted from small to large bolt pattern. That's where I'm kind of stuck. I'd like to do a disc brake upgrade and that would take care of the front. I'd need to figure out something for the rear. I have an 8.75 rear to install, I guess I'll need to pull the axles. Do you happen to know the back spacing on those cop wheels?
yep, swapped 76 BBP spindles/brakes, 8 3/4 with yukon BBP axles. wheels are 4.25 BS I believe.