73+ disc brake backspacing

Not an expert by any means and not debating, but the dana 60 I had built w/ disc brakes changed the rear track 1" according to the builder , I didn't even check it , it dropped in so perfectly, just had to make my brake lines .
Was cut down from a pick up rear -----------

Rear disks pretty much always add width to the track. And with a shortened rear axle it could be anything. The wheel info I gave was for the front anyway, which is what the OP wanted.