Remove the rubber air horns from the air box and put it back on. Use clutching called out for the ultra not the xlt. The ultra is way more powerful. I have 18 as the top gear and the largest you can fit on the bottom either a 40 or 42. You will need a 66 chain I think. Polaris sells them. Places like babbits online can get them. I think dennis kirk has an after market 42 that fits...maybe. at 18/42 I still have more top end than anything else on the snow. Keep in mind you are turning the engine at 8700 not 8000 and snowmobiles were geared stupid high for lake racing. If the clutch components are old, use fresh hardware. There is nothing worse than chasing clutching problems with worn out springs and bushings.