This might be a silly question...but have you screwed down the knob on the proportioning valve prior to bleeding the rears?
Rotate the knob clockwise at least ten turns, then try bleeding the system again...
Also, I assume you are using the old "have a buddy press the pedal down then crack open a bleeder" technique? I stopped doing that a while back...I now use a power bleeder with a plate attachment that covers both master cylinder reservoirs....pump it up with a full load of fluid, then starting at rear open each bleeder until a full stream of fluid comes out.
Makes bleeding a one man process...
If this gets your brakes functional, back off the proportioning valve knob conterclockwise 8 turns...then give it a little test drive....
To increase rear brake pressure turn the knob clockwise until the rears lock up a little too easy, then back it out one turn at a times until it feels good for your driving style.
