64 Dart Gt 4 speed won’t shift into gear ??

If the car is safe to get under, have someone push the pedal with the engine off and watch the action.Is it a clutch or transmission issue. That's what you are looking for.
I’m not to sure to be honest. I would drive it and shift with no issues but I wanted the trans to get rebuilt because I just got it and I wanted to make sure everything was working in good order. But once I install the trans and started it up I couldn’t shift