Hello Borri! Looks like we have both been searching for the same man. I have been looking for probables since the early 1990s, and no success yet.
Hearth tax I have tried, they wont help, although, over the many years, there is one interesting connection, which I will go into later. The original marriage record is in the Oxford Archives, and shows both Francis and Ann (nee Stuart) signing (with an X), in 1787, and as you say prior to that the trail goes very cold.