The 112 is one of the most common models, and the variable drive is what makes it a 112 (that and an oem 12hp Briggs). A 110 would be it's kin, and came as a 10hp 3-speed. The variables sold like hotcakes, but the drive is very prone to belt and linkage wear and operator error/adjustment. They can be difficult or impossible to make work properly, and I'm not sure if there are more fans or enemies of the setup. Solid tractors, otherwise. A popular mod is to disable the variable all-together.
The tiller is actually a 32" model...same as the roundtop previously mentioned, but with different tin. It has a more complex mule drive than the later and more pricey, 36" models. You will want to make sure you have that COMPLETE mule on the tractor. There's lots of bits and pieces that often go missing over time. A bolt-n-go mule will fetch up to $150...a complete tiller/mule around $150-200 (unless you live in WI, where these can go for much more for some strange reason). Peek at the bottom of the drive case on the tiller...they tend to wear thin there from use, and will eventually leak and let dirt in. Yours looks damp there from the picture, but it could just be from the case seal.