cant get front brakes to work

[del0075]

i have been a member a for a while, just kinda looking around at the builds and old trucks. but now i have a ????. and was wondering if somebody can give me some helpful advice of what to look for or do....... this is what i have..... 1971 gmc 3/4 ton 4x4, i installed a new 383 stroker in it, while i was doing it i decided to rebuild the front end and put new brakes on it. it has been setting for about 12 years, i have put new power booster, new calipers, new master cylinder, new proportion valve, and new rear wheel cylinders. i have really good back brakes, but i have no front brakes, i have also replaced the new master cylinder, and front brake pads, thinking that may be it. i have never had this problem before, and i am now baffled, any ideas would be much appreciated.....