[Nasher]

Gaz

I think they go through the swingarm in a different place.
When I was building up my 900SS I compared both.
You may be able to use a M900 set on a 900SS with some silencer mount mods, but not the other way around.
The SS arm has a big open hole at the front and the pipe goes through the middle.
On the Monster arm it has to squeeze through the small hole left between the various webs on the left hand side and further back.

I'll load some images of the two arms into postimage and show you.
Give me 5 mins

Nasher