You might want to email TTR400. He was working on fitting one a couple of months ago. If i recall there is some fab work needed and he also thought it was a bit too long for the 400F.
Not sure how TTR's coming along, but I'm interested in the idea also. You don't see many NSRs in the states, so they are rare parts. Had a guy looking for one in his parts stash in California but he never got back with me.