72 pickup brake pedal goes to floor

[swiny20]

Ok,(72 disk/drum) try to make this short, bought truck knowing it had rear wheel cylinder leak, assuming this was also related to pedal, I have since replaced rear wheel cylinders and brake shoes. I have bled and bled these things (all 4 corners), but no change in pedal, with little resistance it just goes to the floor. I'm new to this site, but I would appreciate any advice. Things I have checked from reading other post. Brakes are adjusted so drums barely go on, combo/poportioning valve button(?) pushed in., and bled the @#it out of them.