Can I use a master cylinder off a car with disc/drum on a disc/disc conversion?

I 2nd post #6.

I also 2nd post #10. True that factory disk-disk cars don't need a prop valve, but that is because they carefully selected and tested caliper sizes to give optimal braking, and that only works if you stick w/ OE spec tires. I doubt your system will be so optimized and you might have wider tires in the rear or such. A rear adj prop valve lets you fine-tune the braking. Keep increasing the rears in a wet parking lot until they lock-up before the fronts, then back off. BTW, rear disks are not needed and mainly for bling, even in new cars.