Don't make it harder than it needs to be.
How ya been Bob?
If you don't remember:
I have stock G-Body (metric) front calipers, 68-72 A-Body rear drum brakes, M/C from an '81 C-10 P/U manual disc/drum setup (aluminum/plastic), NO differential valve(s), no residual valve(s), nothing, and the car stops as well or better than it ever did at 126, holds better on the starting line footbraking, (which is admittedly weak anyway, the 9" x 2" drums aren't a hot setup for that) but the balance of the system is great, it will lock the rears slightly before the fronts when making a hard stop. ( I raced a short, short shutdown track for 2 years with this setup)
The only trick was grabbing the M/C, pushrod, and rod retainer from a junk truck, only modification was the length of the pedal rod, but MAKE SURE the pedal rod is positively retained into the M/C, whatever you do.......
Some of the 88-92 S-10 P/U truck stuff will fit in as well.......