73 Duster Brakes do not work

Ok guys, I installed the New master Cyl and booster. I bled the mast cyl and bled the brakes. I could instantly feel a nice soft pedal (like my truck) but it goes to the floor. I drove it around the block and it stops a lot better and I don't have to push as hard but it still goes to the floor. The Booster has a three prong valve and I am not sure which valve the vacuum line attaches to. Any Ideas? Thanks

B