What are others here with old machines doing for lead substitute ?
I run Avgas
But it's really not critical. They'll run for years on pump gas with no ill effects.
A thing you can do which is cheap and helpful is run a little MMO in the gas (like maybe 1-2 ounces per tank) I would expect that to mitigate any small amount of valve seat wear. I *know* it helps prevent valves from sticking.
One of the less good design features of the T head is that there's not great lubrication of the valve stems. The engine generally runs cool enough that it won't keep the carbon burned off, so it builds up. Especially if the machine isn't run for a while and stopped with the exhaust valve open, you'll find it's prone to sticking.