Converting 68 Valiant Rear to use 15" wheels

A) All day long, put an A body 8 3/4" and put LBP axles from Mancini in it.
Then install 15" wheels that are matched.
Is the disc brake conversion telling you that you have to run 15" wheels for caliper clearance, or are you being told that by someone else?
I installed wilwood front discs on my 69 Dart and just put 14" magnum 500's on it and they cleared the calipers. I had 15" steelies on it and was concerned the magnums wouldn't fit, but they are fine. If there is a slight rub, you can grind the caliper down for clearance, but that is not always preferred. 4.75 is GM bolt pattern.