Master cylinder
 

Can I use a drum/disc master cylinder on a drum / drum car

No you can't the section that you hooked up to the disc portion would give to much fluid & pressure & cause the brakes to be out of balance which would cause one of the set of brakes to lock up harder then the other set .

Residual valve only for the rear and the amount of fluid pushed to the front would be issues I believe.

thanks guys