The 600 K1-K3 master cylinder is the same but I'm not sure about the 750 and 1000. If they share calipers (don't know) then I'm sure they will be.
and don't forget there's probably a "Donor bike" in the Bike park at the meetings if you're really stuck. of course you have to convince the owner that it would be a good idea to borrow his forks/wheels/ subframe/ exhaust and you're going to have to swap them over for him at the end of the day... and don't crash or you'll have to drop his bike off for him on the way home too!
C