There are inherent limitations to a Snowtrac that make power increases only beneficial to a point.
The layout of the engine compartment pretty much limits you to a single, center mount carburetor. So, a Zenith or a progressive Weber are your most available options. Either of those will require LOTS of intake manifold heat and a warm air inlet for the air cleaner. Probable custom fabrication there cause no one manufactures an appropriate air cleaner.
More displacement will quickly get you more power, but the single carburetor will somewhat limit your rpm range. You'll find that even a nice-running 1776 or 1835cc engine will make 1st and 2nd gear almost useless because they are so slow for the power you have.
Build one of those engines with a low rpm/torque cam, pretty substantial compression (because the air is thin at elevation, and the VW is a pretty low compression engine in stock form), and USE A COUNTERWEIGHTED CRANKSHAFT! (Because you'll actually be using the engine's power potential for more of the time and a non-counterweighted crank will beat the main bearings out of it quickly in that scenario.)
Now, you'll want to change the gearing in the transaxle AND the sprockets. Because changing the sprockets gives you more speed (which your newfound power is capable of) but magnifies the jump between gears (which is already too big for deep snow use).
Project Creep will now have set in pretty severely, so you need to define your goal and budget priorities and STICK WITH THEM.