[Flathead Fever]

I was a fleet mechanic for 30-years and have bled hundreds if not thousands of brakes. Every once in a while, you get one that's a pain in the butt, it's hard to get the air out of it. I would go ahead and adjust the rears as close as you can, you can go back and finish the rear adjustment once you have the brakes bled. Don't forget that the rear early Ford rear brakes you used have the long shoes towards the front, the opposite of every other drum brake on the planet. Adjust them up tight and then try bleeding the brakes. If it still causing problems, they make a visegrip with smooth edges that is made for clamping off hoses. Clamp off the rear brake hose and see if the pedal comes up, that way you can tell if the air is trapped in the rear or somewhere else. I have plugs for the master cylinder too. I can remove the lines and plug the holes, and the pedal should be rock hard.

When you bleed brakes pump the pedal slowly not fast. Pumping it fast can break the air up into tiny bubbles making it harder to get it out. You want to slowly push the air down the lines and out the cylinders.