Andy, if you have a service manual, check out the section showing the use of a Manometer for a diagnosis. An HH100 that produces lots of blow by, it is almost always caused by worn rings. You may find the cylinder worn beyond the acceptable limits, maybe not. The piston will also be burned at the top land, enough to see part of the top compression ring, toward the valves. The top land is smaller than the rest of the piston skirt by design.
I think you will want to locate a new head gasket, then pull the head to check the marking on the piston and check the part of the cylinder you can see for size and condition. Then start looking for new parts that might be available. Tecumseh used to offer a .040" oversize piston and rings, but probably all sizes are difficult, if not impossible to find now.
You might be able to locate another Deere specific block to rebuild if yours is way out of limits, or oversize parts can't be found.
Unless the valves/valve guides are really worn egg shaped (+.005-.010), don't worry too much about them causing a lot of oil usage. Oil drawn past severely worn valve guides will show at the exhaust pipe.
How do you use this tractor? If it's your one and only weekly mowing machine, keep up the "topping off" of oil as you decide how to solve the engine problem that best suits your time and economics. Let us know how it's going.