Drum/Drum vs. Disc/Drum Master question

[SubUrban Legend]

I'll apoligize in advance, but I've been searching the board for hours (days) looking for an answer..

I have a '70 K10 with manual drums on all 4 corners and am trying to upgrade with a C20 disc/drum master (new) and booster (used), using the original drum / drum distribution block.

I've read that there is a residual pressure valve on the disc/drum master to keep pressure on the rear shoes, but since I'm keeping the front drums (for now) will I have to add a residual pressure valve to the front circuit, or use a drum/drum-specific master?

I've also read that someone used a disc/drum master on a drum/drum system successfully, so.. I could use some real-world feedback on this one.
Regards,
Mark