Manual disc brake master cylinder?

Just get a MC for a 73 and newer power brake a-body BUT run it manually.
On my 68 (73 disc brakes & 10 X 2-1/2 rear drums), I've tried 1-1/8, 1-1/32 and the 73 PB cylinders. The 73 was the sweet spot for me.
That Dr. Diff setup is a good deal.