Residual pressure in drum brakes is to maintain load against the return springs on the shoes. Removing it from drum brakes causes an increase in fluid needed to apply the brake. It causes spongy brakes and for front disc cars the appearance of no rear brake at all.
Under normal driving you wouldn’t miss the rears. In a panic stop you will know they aren’t there.
Original master was 1 1/32 and are available new on rock auto and other places. Guys all over FABO discuss the right master cylinder for your car in detail. Please read them. Lots of great advice. Smaller cylinder means more travel but lower pedal effort. I’ve used the 1 1/32 master on all of my manual disc brake cars and liked the feel. Currently they cost around $60.
For your safety though don’t eliminate RPV on drum brakes. It is necessary. On the other side it causes disc brakes to drag so it shouldn’t be on a disc.