[Knorm65]

I wrote you a step by step here.

https://www.opelgt.com/threads/any-good-write-up-or-video-of-replacing-a-clutch-in-a-%E2%80%9872-gt-with-a-1-9.116684/post-1509186

The spring is not inside the driveshaft. It is inside the transmission tail housing. If you’re missing it you will need one. OGTS makes them.

The top bolts can sometimes be reached with an impact and long extensions through the shifter hole in the body especially if you remove the trans mount and angle the engine and trans down on a jack. Otherwise cut down a cheap 15mm wrench and get them from the top. Cussing and a breaker bar is sometimes required.

 

[Knorm65]

Those bolts are sometimes absolute hell. You’re just going to have to get creative. You will likely have to find someway to get it with an impact wrench, or you’re going to have to loosen the motor mounts to get you some more drop. There’s a hundred things that may work to get those bolts broken free. The fun part is finding the one you can do with your tools!
Take a break and give it a try another day if you start getting frustrated. Oh and use anti sieze when you reassemble

You do not have to remove the bolt facing upward into the block. Remove all others.