There is a conversion kit out there to swap from small to large mount. Requires a flip of the chain tensioner stud, new chain guide plate and new bar studs with a shoulder to match d009. I have both styles on the two 6800/120si's that I own.
So since we're on the topic... I was fixing up my 6800i (same as 120si basically), and I tested my compression with 2 guages after new cabers and a great looking piston and cylinder... 120psi is what I got on both. What are you guys getting on yours???? 120psi seems low to me, and the rope feels like a lot more than what the guages are telling me.