Marty, you ought to ask your dealer about them, although I've found that most dealers in my area don't have or know much about them. Tisco has a category I top link, part number HTL2102; 20 inch retracted length and an 8 inch stroke, Baileynet.com has a couple of category II top links listed on their site, or you can buy a double acting hydraulic cylinder and add the category I ends to it (whoever does that better know what he's doing to weld it strong enough, not damage seals in the cylinder, etc.). But then of course, if you don't already have hydraulic couplings at the back of the tractor, you'll need a valve and hoses. There are kits available for some of the bigger tractors, but so far I haven't found such for the smaller ones like we have.
Bird