Mike B - from Dave Kirk's web site, the drain plug... "Size is 3/8 - 18 taper pipe thread, commonly used on many small engines. This plug also fits Kohler AQS (Quietline) engines that use a flanged 3/8 - 18 straight thread plug. You'll find the taper thread eliminates leaks and there's no finicky gasket to replace."
If you can get the Fumoto drain valve or something else to route the oil drain away from the engine, that would be a nice improvement. IMHO, anything we can do to build on these fine old tractors and keep them going and user friendly, I'm all for it.