Brake pedal has no pressure

So I recently did a disc swap from a 75 Dart (single piston callipers) onto my 70 Dart. The swap went fine, I bled the brakes, but while bleeding them I never really got any pressure in the brake pedal.
Ok so today, before starting the car, I pumped the brake pedal about 20 times and then the brake pedal was stiff like there was pressure, but then when I started the car, the brake pedal just went to the floor as if no brakes and no pressure or anything at all. Then turned the car off, and pumped the brakes a few times and got that pressure back, but then again when the car was running there was nothing. And I don't mean nothing like.. a little bit of pressure. Nothing as in the feeling you get when you have no brakes.
Also, I have power brakes, and when the car was running, if I would press the brake pedal, the car would idle a little higher when pushing the brake pedal in, does that have something to do with the vaccuum?
Could my callipers be seized? Would that explain why I could bleed the brakes but then not have any brake pressure?