Now I can't vouch for this personally, but I have a friend who really can - he has a personal salvage yard, and wouldn't have said it if he didn't actually know for sure -
His message:
"450 trees fit 450's and 500T and can be used as a pair on the 500-550/4's or
ANY 350, 360, CM 400, or CB 650"
I do know the 450 and 500/550 both have 35mm forks - not sure about the offset or width, though.
I have a 450 stem in the shop, but the top clamp is cracked.
bill2