The marriage license is John Dowdan (transcribed as Dowdan; I have not actually seen the marriage license)and Margaret Nail dated 19 March 1788 in Shenandoah County, Virginia.
I too am trying to find information on Moses Dowdell and Barbara Grove. This family seems to have moved to Ohio and then to Indiana.
1830 Whitewater, Hamilton Co., OH-Moses Dowdle p. 276 3-2-1-1-0-0-1-0-0-01-1-1-0-0-1-0-0 This seems to fit his family.
I am having trouble locating most of them. The spellings make it difficult.Dowdell, Dowdall, Dowdal, Dowdel, Doudell, Doudal, Dowdle, etc.
Sons, Daniel and Nathan were living in Liberty Twp., Parke Co., IN in the 1850 census. Two daughters married in Vermillion Co., IN and were living there in the 1850 census. Son, Jonathan Dowdle in the 1880 census in Lexington, Johnson Co., Kansas.