[sunman]

16” Compomotives, GM calipers, Granada rotors lots of us have this.
Your GM calipers are 70s Chevelle 2 13/16” bore size D52s.
They use a 1 1/8” bore master cylinder with booster if you want.
Gut and plug the proportioning valve and add a Willwood valve for rear brakes.
New brackets from Helix or upscale Howe are not to expensive.
Make sure your MC bore is correct and calipers are the bigger bore D52s.
You can adjust for rear size, these are good brakes when set up right.