I do not know how accurate the information is, but on OneWorldTree there is a Thomas P. Dowden born April 3, 1743 in Maryland. He died in 1783 in Kentucky. He was said to have married Sarah "Sallie" Cleland in 1763 in Maryland. He descends from John and Joanna Neville.
It also states that the John Neville information is the same as you mentioned. It gives John Nevill born 1540 and Gertrude Whalley born 1544 and died 1591, as parents of John Neville who married Joanna Porter. Do you believe that John Neville's first wife was Bridgette Thornsby?
As I mentioned, I am not sure if the above information is accurate!
Hope this helps you some,