Usual method is to remove the gearbox from the car and split on the bench, but the company Jocko used in the other thread appears to split the gearbox in situ. I was a bit sceptical, but he was delighted with the results.
On the strength of that, I would probably have a go at the same idea if I was sure the clutch was good. If the clutch hadn't been touched for a long time, you may as well take the gearbox off and do the clutch at the same time.