Yep, similar to the Monster range the 900SS was fitted with an Aluminium arm and the 400, 600 and 750 a steel one.
I'm (Very Slowly) building up a modified 900SS from parts.
The Aluminium arms are sought after, so I purchased one cheaply that had very crudely had the top brace/shock mount frame filled in with sheet alloy.
After many hours with grinder, dremel,and emery cloth, plus cutting a hole both sides and turning over the edges I've ended up with this.
Does anyone want to make an offer for the monster arm?
Nasher