Has been a while since I posted. It also has been a very long time since I owned one of these earlier models but in gas. I might take the vacuum feed off the booster and see if there is any difference.

Also wonder if you have good vacuum to the booster. There is in the later models and probably in yours a vacuum retention check valve in the line to check.

Not a terribly complex system to deal with. First of all in my aged mind. Make certain each front brake caliper is actually on the right side. Bleed nipple has to be at the higher end of the caliper fluid chamber or you are fighting two air pockets.

Last thing that occurs but unlikely. I cannot remember the change year from rear drums to rear rotors. The brake master cylinders will not be the same. Check the casting part number and compare it to a good source. Even a wrong part in the right box is not unknown.

I tend to test things. That tee in the parts view could be an equalization valve. Bad or good it would not give you a low pedal.