Well after fitting new seals to MC and bench bleeding, then refitting to power booster and still no rear brakes i decided to pressure test the rear lines with about 10 psi from the air hose. (SEE PIC) i heard air escaping and found that a "banjo" connection was leaking although the bolt was tight. THe end of the flex line to the rear caliper has anOFFSET
SEE PIC. i had fitted it the wrong way around and it would not seat evenly on the copper washers. So it LEAKED.
No wonder it would not bleed to the rear.
I have just bled the whole system, from long to short using a vacuum bleeder called an "AIRBOY" fitted to each caliper bleed screw in sequence Great piece of gear and "NO LEAKS"
I have no idea how a mustang stops with 4wheel disc brakes, or standard brakes either but now i can fit the steering and hopefully plant the engine and drive this thing.
Well its been a frustrating exercise and thanks for all the tips to help me eliminate one thing at a time. Cant be beaten.
The pedal is now firm.