Need some help with Brake issues

Interesting! I'm in the middle of doing all new brakes/lines/etc on my car hence why I asked. I'm not changing the prop valve...but maybe I should. We'll see. My pedal goes too low before it gets firm so I've got an adjustable pushrod coming for it. We'll see if that helps anything. It's an original 4-piston K-H power disc up front w/ 10" x 1-3/4" rear drums but the power booster is removed. Putting new rear wheel cyl's on it - trying to decide if I should stay with the 15/16" bore like original or drop down to the 13/16" like some people suggest to reduce the propensity to lock up the rears. It has a new 1-1/32" master cyl on it.