Thanks for the input, Jack. I did tear down the original engine and found a broken oil pump gear. Found no other problem nor a hint as to why it broke. Checked my records and confirmed I had put in a new o/p gear in '06. While fixing a coolant leak, a new w/p, gov. gear, and steel gear cam was installed. The overheating problem resurfaced however in the next mowing season.
This time I pulled the heads and found a possible head gasket leak. It seems to control the temp. OK now, but it hasn't had the deck on and worked hard to find out.
It also had an over charging electrical problem that seems to be solved with a new regulator. After looking at what seems like an endless amount of wires and cleaning connections I'm about to call it ready to try.
Probably will be something else, but for now we're putting the re-power on hold.
I think I'd favor a good air cooled twin for this tractor if and when we do it. When they are right, these L/C Kawasaki's are quiet, powerful, and reliable. I really do like them. But as parts become NLA or outrageously priced, ya gotta do what ya gotta do!