48 Chevy pickup wont shift into gear.

[weltertm]

I bought a non running 48 Chevy Pickup, 1/2 ton. Got the motor running. It wouldn't shift into gear. So i replaced the clutch in the 4 speed transmission. I tested it on jack stands. Worked fine except for reverse. While in neutral the back tires spin. I took the truck off of the jack stands and now it is like before and will not shift into gear. Does anybody have any ideas? I adjusted the clutch pedal and it doesnt affect it.