I have never bought anything from the ebay seller you posted, but Stens replacement parts are good and a bit less expensive than Kohler, and you might find a Stens dealer close to you with better prices. Foley Belsaw also has a small engine Wholesale parts and tool catalog that anyone can buy from. http://www.foleybelsaw.com
or 1-800-821-3452. I have one of their kits for a 12 hp setting on the shelf if I ever get around to using it, and have one in a model 100 that I tried to plow up tree roots with at Cub-Arama 2003. Also used the same tractor to play with at plow days in IA, IL, and PA - wide open, 2nd gear and the engine is still good, so I guess the kits must be pretty good. Tear the engine down before you order a kit, and be sure to measure the bore in more than one place - top, center, and bottom. Kohlers will wear the cylinder in a taper and it may take more of an overbore than you think to clean it up. The rods are only available in std and .010 under, but you may be able to turn the crank .002-.003 to true it up and have a standard rod resized, without going to .010 under.