If your rears locked up that would make me think there was a problem with the fronts originally.

If the pedal is still spongy you may be bleeding wrongly .... the proper proceedure is to bleed the furthest from the mc first....but first make sure you have fluid in the mc res... then pump up the brakes until you begin to get some pedal, then open the bleeder while your partner pushes the pedal down, then shut the bleeder and let the pedal up and do again. Repeat until no bubbles come out of the bleeder.
then go to the left rear and then right front and finally lf.

Of course if you are in England do the other side first.

Good luck.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.