master cylinder 4 discs, 73 dart front / mustang2 rear, manual

I was talking to Cass (Doctor Diff) last week about this since my son is doing a rear disc brake conversion on a Ford 9". We already had one of the aluminum MC's he sells (essentially same as Mancini unit) and he said it would work fine without any mention of stroke or volume. He said they're essentially a 4 wheel disc brake MC (don't have the residual valves that disc/drum MC's might have). I don't know about the Mustang II calipers, but the GM metric calipers used in the conversions will need a proportioning valve to get the correct brake bias.

I don't think you'd like 1.125" - too big, too much leg effort for manual brake, even it it could deliver the fluid.
I run a 1.03" on my Duster. (1-1/32"), stock pushrod.
My son will be using the .9375" (15/16") we had sitting here.

http://www.doctordiff.com/aluminum-master-cylinder-kit.html