I just found James and Belva's marriage record on familysearc.org.

Montana, County Marriages, 1865-1950
name: James Edward Gregg
titles & terms:
event: Marriage
event date: 18 May 1917
event place: Havre, Hill, Montana
age: 29
marital status: Single
previous spouse:
race: White
birth date:
birthplace: Kentucky
estimated birth year: 1888
father: Paul Gregg
father's titles & terms:
mother: Marie Charlotte
mother's titles & terms:
paternal grandfather:
paternal grandmother:
maternal grandfather:
maternal grandmother:
additional relatives:
spouse: Belva T. Sullivan
spouse's titles & terms:
spouse's age: 27
spouse's marital status: Single
spouse's race: White
spouse's birth date:
spouse's birthplace: Missouri
spouse's estimated birth year: 1890
spouse's father: Wm. V. Sullivan
spouse's father's titles & terms:
spouse's mother: Etta Caroline Braswell
spouse's mother's titles & terms:
spouse's paternal grandfather:
spouse's paternal grandmother:
spouse's maternal grandfather:
spouse's maternal grandmother:
volume/page/certificate number: 1912-1918 p1308
film number: 1902811
digital folder number: 4350536
image number: 662