Clutch issues. Can't put gear in while engine running

You need to tear it apart. End of story. Check EVERYTHING

Check PILOT SHAFT TO ENGINE CLEARANCE. The shaft may be bottoming out in the bottom of the crank, if the crank is not fully machined

Check pilot bearing fit. This is not easy unless you have an inside mike. Examine the pilot shaft for blue, wear, etc, damage

Verify the pp operates as above. Take it to a clutch shop or put it in a press

Generally examine the condition of all parts. If you cannot verify the clutch, plan on replacing it.

MAKE CERTAIN the clutch disc is installed correctly. The "bulge" side with the springs exposed goes to the rear, to the transmission side.

after that, you can argue with things like "is it the correct bell" for the car, and "does it have" the correct Z bar ball and Z bar, linkage etc etc and fork.