I think removing it to work on it on a bench would be way better than fighting installing the forks, especially the 1st & 2nd gear fork, into the side cover
If you do the work in the car are you going to drain the lube out first? I would If you remove it and work on it on a bench you won't need to drain it as long as the have a spare tranny yoke installed in it so the gear lube doesn't drain out the tail shaft housing while removing the trans
Good luck either way