In my experience, the hardest vehicle to get a decent pedal is the '65 thru '82 Corvettes with the 4 piston fixed calipers. I tried everything. Bleeding brakes should be easy. In desperation, I bought a pressure bleeder (Motive). Dang thing worked like a charm. Not to mention easy peasy...Schwaben Pressure Brake Bleeding System. The pressure release and snap off connector make it easier than the Motive bleeder.
Also, on these cars, make sure you have the carb idle mixture screws set to highest manifold vacuum. It makes a BIG difference.