I think it has more to do with the fuel tank and seat pan than the sub frame. I bet if we all put our heads together we could come up with a way to do it on he 91 though.
Do to my ignorance, I don't know what a seat pan is, I'm assuming it's how the seat fits on. If I could fix that stupid curve then I could make the bike so much more comfortable and easier to ride. It kinda stinks, its either (if you a guy) you get pinched or maybe that's just my poor riding, or when you lean back or jump your always against the seat
But it's something I'm seriously considering doing, then I wouldn't be in such a rush to get rid of my thumper (KLX 140L) an go to a 2-smoke.