Help with brakes

[idastang]

This is a 69 short bed 4x4. In a previous post with a questions about shocks, it got nicknamed mutt and rightly so. As I make progress to get mutt going down the road, every test drive develops a new problem. The issue at hand is the following, after replacing the rear wheel cylinders, the brakes lock up in the rear. I tend to belive this is because they where not working before I replaced the leaking wheel cylinders. So I thought it would be best just to check the complete brake system out. Long story short, replaced front calipers, (front being a d44 from a 76 k5 based on the bom) and since the master was full of crap, id it as being from a 72 with power booster. Ordered from napa part number up 36280. This is a dual bowl with booth bowls of equal size. Just before putting things back together I wanted to check out the proprotioning valve. With some research on this site and others, its a distribution block. Ok I know I will need to now get a p/v, but the question is can I use the current m/c? I don't know if its a disc/drum m/c or a drum/drum mc. I am sure the po is having a good laugh by now I have already bench bleed the m/c, I am not sure if napa will allow me to do a return. If so does anyone have a part number for a disc/drum,deep bore m/c? Thanks for the help.