That makes total sense Pace. I am experiencing that right now.
The disc that came with my Moser Engineering rear has the big Ford bearing and Ford flange on the end. Came with single piston 11" disc brakes. Same caliper as a Cadillac Elderado.
They will not clear my 87 GN steel wheel but my 15" Centerlines fit.
I am also considering 16" GNX wheels but unsure of offset since I have no fender flare. Also tire selection is slim in 16"
Only true GNX wheels will have an offset that sticks out too far, needing flares.
GTA front wheels have a close offset and will work, but to me they looked sucked in a bit.
The GTA rear wheels have too much (positive) offset and will rub the frame.
The 18” GNX style wheels from venders are made specifically for our cars and fit no problem.
I believe the 16” GNX style wheels from vendors have the GTA front offset, but it’s been awhile and I’m not quite sure.
You are definitely right about 16” tire choices.