Rear brakes lock up... front disc

My original brake set up used to always lock the rears up easily; factory manual disc. It was like power rear brakes. '69 Factory Service Manual says I should have a factory proportioning valve on the frame rail back by firewall under the floor board; my car never had that. I drove with these death trap brakes for many years. This rear wheel lock up issue is common with these cars. That is how these cars were built originally.

Now I run the 7/8" rear wheel cylinders (order for rear of '72 D100 2WD truck), MP adjustable proportioning valve, stock combination valve, 15/16" master cylinder (Order for '73 Duster 340 w/power brakes RAYBESTOS Part # MC36406 its a direct bolt on), Goodrich braided brake hoses front and rear, all new metal brake lines, new springs and shoes in rear, reproduction rear drums, emergency brake cables freed up and lubed, and front calipers not sticky and working correctly. Front brake pads are NOS. The car brakes fairly well, rears don't lock up. But when the front pads heat up it takes more pedal effort to slow the car down. In the summer I am not happy with the braking performance at all but rears don't lock up, just too much pedal effort when pads get hot. I just ordered EBC Red pads for the front. Rotors are in great shape so I'll just scuff em up with sand paper when installing the new pads.

I think the combo I have works well and I think with better pads up front I am hoping to finally have this crappy brake set up licked.