Hi Diane -
I have a marriage from Canney's "Strafford County Marriages," p. 907, for Enoch Stevenson, m. in Tamworth NH 7 Oct 1810 to Lydia Dow. Both of Tamworth. Two of Joseph Warren Eastman and Nancy W. Stevenson's children were Enoch and Lydia. Sounds pretty close, and the dates seem to fit.
William Eastman of Tamworth married Betsy Dow. She was born about 1758. Her parents Jeremiah Dow (1733) and Martha Goodwin lived in Tamworth in later years. I wonder if one of Betsy Dow's brothers could have been a parent of Lydia. Of of them, David Dow, married Lydia Young. Other brothers were Samuel m. Hannah Wadleigh; Jeremiah b. ca 1763, m. Elizabeth Perkins in 1786; Ebenezer, d. 1844 in So. Tamworth, m. Hannah Page, and Charles m. Martha A. Gordon in 1790. There aren't many dates for this family. The Dows were early settlers in New Durham, NH. There is a book about them called "The Book of Dow," that I got on loan from the New England Genealogical Society. You might also check Rootsweb or the Eastman Genealogy on the web to see if some of these names pop up (I'm sure the Eastman Genealogy on the web has Joseph Warren's line, and you may have seen that already). My interest is in the Eastman family. I've been searching collateral lines in the hope that I might be able to connect that way, so have gathered quite a bit, and am especially interested in Tamworth. Hope this helps.