A recent purchase of a 160 degree thermostat and gasket from my friendly Kubota dealer revealed one new part number. The thermostat itself is currently still 19203-73010, but the gasket has been changed ( again... ) to 16851-73270.
A good parts guy can eventually cross-reference from any of the original numbers, but the current number makes it a little faster at 4:55 PM on a Friday afternoon!
John
The thermostat parts numbers can be found here: http://c34.org/bbs/index.php/topic,3133.0.html, among other threads. (Stu)