Did you bleed the whole system, or just the fronts, or not at all? Any leaks? If you didn't bleed the brake system that's your problem. Start the bleed with pass side rear, then driver side rear, the pass side front, then end with the driverside front.
Or, if the pedal is firm but the car just won't stop, you might have a siezed caliper.
Did you mess with the master cylinder or booster at all? Might have a vac leak at the booster or a bad booster all together, or a bad master cylinder.
when i did mine it took me doing it alot to get a good pedal. i started on the back pass rear then back drivers then pass front then the drivers front. i did that about 6 times before i got a good pedal. i did a new mc,front aerospace,and wilwood 4 piston rear, line lock. i used alot of brake fluid
I had drum rear. 98 style cobra front calipers. Never touched the mc or booster. I need to buy stock front brakes again. This simple brake swap turned into a nightmare. Back to a termi for me.