OK I spoke to 77 yo Alan Craig today, a SUZUKI Dealer from the mid 60's to the late 80's.
Alan sponsored a young Peter Carney on RM80's then RM125's
He also sponsored Chad Reed on RM80's before me.
Anyway Alan's best memory is twofold,
Peter's first year of 125's was the C model, but SUZUKI also gave him a slightly used B model that was fitted with the alloy arm as a practice bike, Alan's memory was the last shipment of B models had the alloy arm in the bike but it was not a floating rear brake. He did not retail any.
Peter went on to win the KID MOTOCROSS series on that C model.
SUZUKI gave Alan lots of trick parts for RM125's including ex Gaston Rahier titanium parts which Alan eventually gave me.
I have stayed out of this debate but I did have RM125 A,B and C's
I believe that there is no advantage in the alloy arm, I believe shocks with adjustable compression and rebound dampening do give an advantage, as does gold valves forks,
What would happen if someone turned up with an ex Gaston factory arm in his bike, how would he prove eligibility ? what if that arm was copied and readily available ?