I didn't realise it was as obvious as bolted on or splined shafts.

I know the 2wd/4wd thing, mine is 2wd but has a lot of 4wd bits and god knows what over the years as was built as a track car, so wanted to be sure.

And yes, viscous diffs arent great even new, once old they're rubbish, this one could be either open or a knackered viscous, its hard to tell.