I have a 1983 Z28 with a 5 speed manual, When I start my car and press the clutch all in and I engage in the 1st gear it won't go in at all I have to force it in and I'm having the same problem when I use the reverse gear it grinds. I also get a whiny noise I think coming from the clutch when I start to release the clutch up when I have it in 1st gear. I will post a video of this to help out. thank you for your time to read this have a great day.

 

Sounds like a countershaft issue like countershaft bearings.

 

Sounds to me more like a clutch problem.

Clutch is not disengaging completely. Especially if it crashes other gears during hard shifts.

My bet would be on the pilot bearing/bushing. Effectively, part of the clutch system. If there's excessive friction there, it acts JUST LIKE the clutch doesn't disengage completely.

Pop the trans out and the clutch off and take a look.

 

The 83 and older models had mechanical clutch release linkage that is subject to wear at the.pivot points, stress cracks, and other simple but common issues. You may want to thoroughly inspect the linkage, including watching the linkage while someone else presses the pedal so you can see flex or movement.
You may find other clutch problems that need addressed but slop in the linkage will keep good other parts from working well.
I had an 84-up T5 setup with hydraulic clutch release. I then tried mechanical. The hydraulic was better IMO.