Just buy the gasket, from John Deere, along with new T-stats. 

If the old gasket, is easy to clean and remove, I've changed both T-stats, from the right side of tractor, and only drained down a little amount of coolant. (No lifting of the steel hood)

Used a mirror and flashlight, to unsure I got the surface clean {and the grooves the T-stats sit down into}, on that upper water manifold; and then the upper cast piece ( that attaches to the upper Radiator hose) I removed it, put in a vise, and "flat-filed" it with a larger file, to insure its surface was flat, for the new gasket.

Make sure, those NEW t-stats, stay in their counter-sunk grooves, when reassembling.