No Brakes!!!!

[WreckItRoth]

So recently my 03 Aleros oil pump went out and the engine isnt worth repairing. Im using it for a parts car on a current swap I'm doing. I got an 03 Grand Am and the guy told me the brakes had an issue so i got the car for 400. I started by swapping the calipets from the Alero and then got new pads and rotors all the way around. I converted the rear end to disk while i was at it (my Alero had them) and proceeded to do the regular work (bleeding lines and so forth. The pedal got firm while the car was off but as soon as it starts the pedal goes straight to the floor...
I heard a slight hiss under the hood and thought the master cylinder and booster were out. So i changed those off the Alero onto the GA. Then tried again and the same thing. I checked if i had vacuum and i did. So i changed the proportioning valve and proceeded to bleed the brakes again. The pedal feels much firmer while the car is off but again when vacuum is drawn i lose all pressure. I changed every single piece of the braking system except the original lines. Still as soon as it starts straight to the floor and no brakes... i dont know where else to go with this and figured I'd ask for anyones opinions on the subject. Ive never experienced a brake job this frustrating.