This tractor does have a live clutch, two stage. The turnbuckle is the only external adjustment that I know of. If the adjustment doesn't do it, stand by for a expensive split. Two clutch plates, two pressure plates, pilot bearing and throw out bearing. Sounds like with the drive that far gone, unlikely it's going to have the room to adjust. One other thing it could be, but requires a split to check, is the splined drive coupling. But if this splined coupling stripped you would hear lots of noise when the clutch is let out.
Chris