You have to make sure the rear drums are adjusted right or you will not get a good pedal.
I had my whole system drained as part of my cab off frame rebuild.
I started with the used master and booster from my parts truck, it rolled on it's roof so they had to be good right ....... don't bet on it.
Anyway I replaced the rear wheel cly. and all related parts for the drum brakes, front calipers with new pads, all 3 rubber hoses.
After gravity bleeding and getting fluid at each wheel I then used a Snap-On tool vacuum bleeder that uses shop air to pull the vacuum.
Pedal was piss poor at this point so had a helper bleed the 2 man way and they got a little better but still a low pedal.
This is when I found the parts truck master & booster were bad so I got a new set and again pedal was low?
I did look into and adjusted the rod but did not help.
What did help a lot was using a pressure bleeder and push the air out. It works on 10 psi but that is all it took to get a working pedal. It is still a little low for my liking but the truck stops and that is what counts.
Dave ----