Our Rufus was born in Hartford, VT and lived many later years in Orford, NH. His brother David (#512) born 6 Jan 1796 is found on p. 471 in Charlotte Whitcomb's book. This David married Lucy Prouty and moved to Ottumwa, Ia. Their Parents were David and Ora Richardson whe farmed in Hartford, VT.
The coincidence of both our Rufus and your David living at the same time in the small town of Orford is very intriguing. I could find no match for your David in Charlotte's book.
One good research place for New Hampshire late 1700 and early 1800 ancestors is the Bureau of Vital Statistics in Concord, NH. There birth and some death records contain names of parents. You can look through the record cards yourself.
The Whitcomb Wheel is a new publication and its editor is attempting to update Charlotte's book. Try contacting him, Jeff Linscott at email@example.com
If you have more data about David, let me know.