Hi craig.a, and a warm welcome to the forum. It's great to have another Scott Bonnar owner on board.
The cotter pin is captive: it cannot be removed, it can only be loosened; then the clutch can slide off the crankshaft extension (PTO). To remove the inner clutch half, just undo the nut a few turns and gently tap the cotter pin down. When it releases, you can then remove the clutch half from the shaft.
You then push out the thrust bearing from behind.
