How do you and how much do/can you adjust the MC rod that goes from the power brake booster to the MC? My pedal bottoms out too soon and I'm guessing I can adjust this rod so that brakes work a little sooner in their travels.
In my '70 the rod isn't adjustable, I don't think yours is either.
Does the pedal bottom out shortly before it hits the floor, of 1/2 way through the stroke?
Could your problem be related to old lines ballooning or air in the brake lines?
The MC was never bench bled priot to installation but I've bled the brakes about 4 times im 6 years. There could still be air in there?
Getting back to your original question, if the pedal is going to the floor, can you pump the pedal to build pressure or some pedal height? If yes, then probably air in the system, but if no, probably if equipped with rear drums, they need to be adjusted.
If I pump, it still goes to the floor. The car does have rear drums? How do I make this adjustment?
If you pump and it still goes to the floor, it would seem to me that you have other issues on top of the rear brake adjustment. Even with the rear brakes completely out of the picture, you should still have some braking ability on the front brakes if you have the dual reservoir.
Apparently you have brake fluid going to the front calipers if you were able to bleed them, but even with air in the lines, you should be able to build up some kind of pressure and keep the brake pedal off the floor.
Try pumping the brake pedal while someone else tries to spin the front tires by hand to see if the tires will even try to stop. If they don't stop, then more than likely your MC isn't directing enough pressure to the calipers. I assume your calipers are new? Can you see if the caliper piston is moving while you pump on the pedal?