Quick Backspacing Question

Dart66, Are you running a stock rear suspension? No wheel tubs or leaf spring relocation? Also is this on a 70+ Dart or a pre-70? I may be wrong but I read somewhere that the older model darts had bigger wheel wells. I may be wrong on that though. If so I'd like to run that. I am just trying to fit a comfortably big tire in the rear with no modification to the tubs or having to relocate the leaf springs. I read a 225 would fit flush on a 8" wide wheel.

As for the bolt pattern, how much would it roughly cost to do a complete swap to a bigger bolt pattern? (roughly)