Even with offset shackles 6.5" backspace will move the tire too far in. I think you'll be better off with something like 4.5" backspace.
I'm planning to run 15" Centerlines with 4.5" backspace but my '69 Dart has a B-body 8-3/4 rear and I'm going to get it narrowed to perfectly center the wheels in the wheelwell.
I'm sure other FABO members have more experience with this so let's see more replies.
