Hang out in the garden tractor pulling circles and you'll hear plenty about Kohlers, especially the old iron-blocked K-series. Vogel Manufacturing makes a lot of parts for them. You can even get aftermarket iron blocks. They are, IMO, some of the best engines out there. I think even Hondas are less expensive, though.
The XKE overhead valve was well thought-of, although not that popular in the F200 kart class. It was more substantial of engine than its competitors like the GX200, OHH65, and Intek/Animal/World Formula/whatever. Only Briggs and Honda have survived the brand wars. Tecumseh went under completely and I'm not surprised after seeing the insides of an OHH65.