Brake question (long)

[joescott]

Hello all
I have a 1967 GMC ½ ton lwb pu. In November I got the truck back on the road, but the brakes did not seem to work properly. They would eventually stop the truck but were very hard. The truck has 4 wheel drums by the way. I have replaced the MC, all 4 wheel cylinders, all shoes, all rubber lines, and front hard lines. Because the truck has all drums, it uses a dist block instead of prop valve, but I cleaned it out anyway. I have bled the system using the pump method, also used a vacuum pump at the wheel cylinder and pressure bled from the wheel cylinders. I adjusted the brake adjusters to the point of a hard to turn wheel. The pedal is very hard with no signs of sponginess. All four wheels will stop when the truck is on jack stands. When on the road the truck still feels hard to stop. It does stop but I worry the seat mount bolts will break with the effort I have to push on the pedal.
Today I am going to a junkyard to find a booster to convert to power brakes. I have read on this board that some trucks use the front reservoir in the MC to run the rear brakes. When pressure bleeding I confirmed the rear brakes are connected to the rear reservoir and the front are connected to the front. Is this correct?
Thanks in advance.

Joe