If you plan on running tracks on that machine you can't go any larger than 21" tires, and you'll have to have wheel spacers. Is there enough of your drive belt left to get a part number?
You should go ahead and go through the T-20, they are pretty simple, and Mike's guide in the articles section makes it a breeze. You can call Recreatives Industries and get any parts you need for it. At the very least you should put in new seals, gaskets, o-rings, and fiber thrust washers.