Hi Lynne,
Looking at the Lee's of Hillfarrance, it appears William Lee born 1766 actually died in Hillfarrance in 1840. He was buried 26 Dec 1840 aged 73 years (giving an estimated birth year of 1767). Several of his brothers remained in the town as well, and these were the only Lees there. Therefore I don't think we have the right family for our William Lee alias Dyer. Sometimes things appear an "almost" fit, but it just doesn't seem quite right.
I still suspect there is a reason behind that name change, what it is we have yet to find out.
Thanks for sharing what you have found, it is useful to explore all possibilities and eliminate any that don't work out. I wouldn't discount Devon either, as it is where he and Mary Pulman were married. She was from Cornwall.
Cheers,
Kells.