A track will certainly be one barrier. Your track is 13.5" wide x 129" long. When people talk about cutting down a track, in this instance their referencing the width. You would take a 15" wide track and remove .75" from each side (1.50" total) to bring the width to 13.5". If you still have the stock SnoPro drivers you'll need the track to be 3.0" pitch.
The next barrier will be what to do about the suspension rails. You'll need extensions or longer rails to accommodate the track length you choose. Extensions are likely going to be super rare at this point. Longer rails would probably have to come from a F7 EXT (144" track length). I'm not sure what kind of work is involved in making that change; if all the holes mount up in the rails and such.
Then there's the tunnel, and whether you'll need an extension or not. If you go 144" + track length, I would speculate you'll want to extend the tunnel some. I'm not sure that you'll find an extension to purchase; this might have to be fabricated out of some light aluminum like the factory tunnel.
At the end of the day, IMO, it still won't be a great off trail sled. The narrow track on these lends itself to trenching, even with added track length. For the time and money involved, I'd look at keeping the SnoPro stock and find a Crossfire or the like for deeper snow days.
FWIW, I've lived the shortcomings of the SnoPro. Super fun sled, but not great on the deep days.
