Jennifer,
I still have not found any think to link Hiram and Calloway, but did find James Calloway Capps on FamilySearch.org.
Information found (so you can cross check)
James Calloway Capps born July 1819 died 7 October 1903, buried Upper Camp Creek Cemetery, Muldrow Oklahoma.
Father: Willis Capps, mother: Elizabeth Jane Yadon
Elizabeth Jane Yadon Capps parents listed as: Joseph preston Yadon and Susannah Mary Pennybaker.
Jmaes Calloway Capps married Havey Bell 16 July 1840 in Camden County Missouri.
Havey's birth information listed as August 1823.
Havey's parents are not listed.
Willis listed as born: 11 Mar 1780 in North Carolina
death 10 Mar 1855 in Camden county MO, buried in Roach Cemetery.
Thomas Capps Born North Carolina.

Willis's Father is listed as Thomas Capps.