The same thing I did last time I needed snow mobiles. Use the stats of motorcycles from the basic set. Its simple-- but how close are they really?
This is the second time I'm doing this, and I expect it to matter more this game, so I started looking up stats. Snowmobiles are actually really fast. Maybe even faster than the bikes, though that may be only under ideal conditions. The enthusiasts also claim they accelerate faster than motorcycles. So we can leave those numbers. Snowmobile's range is a lot lower than bikes: they get terrible gas mileage, so we'll halve the range. They're also a bit harder to handle than motorcycles, but they're more stable. So -1/+1 to Hnd/SR. The weights seem to be in the correct ballpark, and the costs aren't bad either. I'm not sure about ST, so we leave it there.
So to use a motorcycle's stat-block for a snowmobile
- drop handling by 1, raise stability rating by 1
- halve the range
And that's it! You have a range of snowmobiles! I hope you find this useful. Its a fairly quick and dirty conversion, but it seems functional enough. If I'm weird and the only GM who ever ends up using snowmobiles in their games, I hope I have now inflicted the need to use snowmobiles in the game upon all of you. Happy adventures in the snow!