WHT may refer to William Henry Trant.
Who died in 1859 and is buried in St Saviours, Tormoham.

The reason I think it may be him is that in a Newspaper Article in the Exeter Flying Post of 9th June 1859, it says

"An application by Mr Trant to erect a fountain near Meadfoot Cross was acceded to, the work to be done under the direction of the Surveyor"

And he is the only Trant that I can see that may fit.

Of course this is only supposition, so WHT may not refer to him at all, but looks to be a good place to start.