Below is the source material you requested. This Eli Duvall is also listed on p. 283 of Newman's book as the son of Henry & Elizabeth. Regarding John, I have a listing for a birth of January 5, 1840 son of Eli & Sarah E. I think this is what you may be looking for. This was posted in the January 7, 1840 edition of the Baltimore Sun.
Please email me at firstname.lastname@example.org. I would like to hear what information you may have and this is my husband's genealogy account and we have separate email addresses and he no longer subscribes to genealogy.com
Eli Duvall Gender: Male Marriage Date: 24 Dec 1833 Spouse: Sarah E. Thompson Spouse Gender: Male State: Maryland County: Anne Arundel
Dodd, Jordan, Liahona Research, comp.. Maryland Marriages, 1655-1850 [database on-line]. Provo, UT, USA: The Generations Network, Inc., 2004. Original data: Most of the records in this index may be found at the Maryland Historical Society or the Family History Library. More specific source information is listed with each entry. Original marriage licenses should be located at the county clerk's office.