Rear disk question

I think the ones SSBC sells are Ford's. It would not be tough to figure out what pads they use. My first guess would be late model Mustang.

Any disc brake conversion will widen the rear track by 1/4" or so if you stay with the small bolt circle axles. If you change axles to the B-body style with 4.5" BC you're going to gain around 3/4" of track width. These are not exact numbers, just ballpark.