In no particular order:
1) I'd get the gaskets, then you can be sure the old ones will never ever tear, leaving you to find these in a draw years from now and wonder what on earth you got them for. Otherwise you know you'll need them and they'll be on back-order.
2) You may well be able to just oil the old tensioners and get them working smoothly again, however, I'm sure some people fitted K3 and later ones to curvies. I believe they changed the design again around K5 or so and the design was in some way incompatible with the earlier bikes, a new oil feed design or something. Perhaps.
Try just taking the nut off the top, and using a screwdriver to tweak the tensioner out and back in again after dropping some oil in there. Could be a very cheap, if not exactly permanent fix
Jambo