Hey drummerboy...my help and suggestions are from the heart and in most cases, very sincere.
Part of how working on old trucks for over 40 years is how it gets into ones being.
You are discovering what most of us "oldies" have found time and time again...rear brake hard lines rust out badly due to the location of the lines...the front end of that pipe is protected from road spray and salt etc by the front cross member.
The hard lines across the rear end rust badly and the rubber hose is subjected to exhaust heat and road wash, including salt etc.
The rear wheel cylinder bleed nipples rust into the body of the wheel cylinders and will usually snap off when you attempt to open them...
My comment about the master cylinder is again based on 40 years of experience,,,
The travel distance of the master piston during normal use is about 5/8"...when you go to try and bleed the system, using the "pump the pedal up process", the travel bottoms out for what may be the first time in 10 years,...often damaging the seals and valves ...
Suggestion:
Change the wheel cylinders on both sides while you are working on this repair.
Check the brakes shoes...and drums...make sure they are in good condition.
Change both rear brake pipes and the rubber hose which blew out.
Fit the new front to rear brake pipe and clips...dont forget the clips...the pipe will vibrate and could fracture if you dont use the clips.
Find, buy, beg, borrow and pressure or suction brake bleed tool so you dont risk damaging the master cylinder rubbers...
Use an unopened new bottle of brake fluid...fluid from old opened bottles often has absorbed water from the humid air...lowering the boiling point of the fluid...
Bleed the rear system drivers rear first, then passengers side...
Make sure all fittings are tight, with no leaks under pressure...
I am assuming you are also changing the front brake hoses...did you check the bleeder nipples in the front cylinders...???
Afterall, you can get away with primer painted panels and "patina", but you should never shortcut brakes...
This board has a great group of folk, most willing to lend a hand...and part of that "help" is sometimes having some fun...for me and some others, we will tell it like it is, prickles and all...
Have fun !!!
