Did you split the cases? If you don't see anything broken or obvious, I'm not sure a schematic would help. There are a few here
A couple times in this thread people asked if the flywheel could spin freely and your answers seemed to be talking about the clutch side moving freely. The flywheel is on the opposite side of the transmission,on the left. It would only spin once the clutch is engaged to start. If it were stuck it would mean that the piston was siezed in the cylinder head or that something was blocking the flywheel. Sometimes screws on the electrical side may back out and jam up a flywheel. This can make it seem like a transmission issue. But if you tore the engine down and didn't see anything weird on the "alternator" side or with the piston and rings in not sure what it could be.
Oh shit, I didn't see you'd figured out the issue in a different thread. My bad big homie (edited)