worst case, just get a track extension, and a longer track. that way when you come back to the trails, just exchange everthing back to the 121 and you'll be good to go.
Rail Extensions from Tracks USA: America's largest snowmobile track dealer
they've got extensions up to 144 for the prox.
a new track and extensions is less than a new sled and or the cost of renting a sled for a weekend.
