The only option I can think of, looking at a used response would be the transmission ratio. There's a 2 letter code stamped on the top of it you can see with the hood open.
The taller frontier tire would be a good upgrade, but might be too tall to wrap tracks around. I like the lightweight briggs in the already front heavy argo. You can add rear axle extensions. I ordered my response from the factory with skid plate and rear extensions.
The new 8 wheeler based on the frontier will be the used machine to buy in a few years. 23 hp briggs, taller frontier tires and all the rest of the frontier features.
To Invent, you need a good imagination and a pile of junk. (Thomas Edison)