Another "brake help" thread...

I've scoured this forum and have done a lot of initial diagnosis based on what I've read, but I'm still dealing with bad brakes, real bad. Here's a breakdown of what I have, and what I've done.

'76 Dart Sedan, factory manual brakes, 7 1/4 rear w/ 10" drums. Discs up front that have been converted to new '82 Dip calipers mounted on the rear (hose at bottom, bleader at top) with speed bleeders on the calipers; need a set of speed bleeders for the rear but they are M6 and not available at the local parts store. New 15/16" MC from Dr. Diff. New pads/shoes/flex lines from Bergman. Rebuilt the drums with new everything, springs, wheels cylinders, shoes, etc. Everything is new in the system but the actual drums, rotors, and combo/proportioning valve.

Feels like almost 90%+ bias to the rear brakes for stopping; I know the rears lock up and I've never gotten the fronts to lock up; at least 10x more brake dust on rear wheels than front. When I pull the drums off, everything is covered in black brake dust and dust falls out of the drum. Almost no brake dust on the front wheels, but the rotors are shiny so I know the calipers are doing something, but not much. Rear brakes are awful loud, squealing/screaming/screeching, drives me nuts. Also sticking occasionally and surging, such that if I let me foot off the brake pedal, the car may not move, it may move slowly, or it may surge because of brakes sticking, then not, then stick, then not, repeating. Perhaps the drums are out of round? But there must be more wrong. TONS of pedal travel before I feel the brakes kick in. I have to pump 3-4 times in order to get what feels like a decent pedal. I've bled the brakes more times than I remember. Originally bench bled the MC on the car, but this weekend I pulled it off the car to actually bleed it on the bench. I pulled on the parking brake cable to ensure it was not creating tension, didn't seem to be. Parking brake system is missing the intermediate cable and the cable to the pedal (if anyone has one, I'll take it). In other words, parking brake levers are not connected to the pedal. No geysers out of the MC when releasing the brakes. I've adjusted the rear brakes multiple times such that I hear a slight rub of the shoes to the drums when I spin the drums. Fluid was flushed after I did the new MC, rear brake rebuild, and new calipers. I don't have a gauge set to test the pressure into and out of the proportioning valve so not sure if that's working right, and can't find details on testing otherwise. Cass has confirmed rear drums are assembled correctly, other than the top washer being upside down but that shouldn't hinder anything. Cass also said the fronts look good, except the drivers brake hard line and the flex line connections are upside down. I have some CopperNickel coming tomorrow and will reorient. He pointed this out saying it could kink the flex line. No evidence of that. Also, no evidence of fluid leaking anywhere. MC is always full, no spots on the ground unless I'm going through a bout of bleeding.

What am I missing? Any other ideas? My thoughts at this point are either a bad MC, proportioning valve, or both. MC is new though. Thoughts? Not sure how to test without a gauge set and that's not something I've seen at local stores. Thank you everyone.