Will it go into gear with the motor off? IF so it may be the clutch not fully disengaging. A clutch that doesn't fully disengage can prevent a tranny from going into gear.
1. Check the clutch adjustment.
2. Adjust the shifter and be sure the linkage is correctly installed.
For your year car the levers on the side of the tranny should all go up unless you replaced the tranny with an OD tranny.
Remove the pins that hold the adjustable swivels to the shifter and place the shift levers on the side of the tranny in the center position. Place the lower rear lever (reverse) in the forward position.
There is a hole/notch on the bottom edge shifter housing and holes in the shift plates (not always in reverse plate). Place a pin (allen wrench works good) in that hole to align the shift plates on the shifter, then adjust the swivels so the rods slip in and out. If you have stop bolts on the front and back of the shifter loosen them, place the car in 1st and adjust the rear one to just contact the shift plates and lock it down. Place the shifter in 2nd and repeat for the front one.
I hope it helps.
PS I am assuming this is a 4 speed.