Many thank! I have a mint m910 rear mech and want to use it on period correct 93 bike. Do long as it looks right. I could see any other differences but my m900 RD are in average condition.The only difference is that the internal spring mechanic changed.
Other than that they are exactly the same, apart from one is stamped M910 and one M900.
M900 was running up to 1994 and M910 was for 1995 only and then superseded by M950