Development and Employment of Fixed-Wing Gunships by Jack S. Ballard is a 326 page book that thoroughly documents the development of the AC-47, AC-119 and AC-130 gunships. The book was published by the Office of Air Force History in 1982, and is the eminent resource for gunship development during the 1960s.

Four key segments from the book provide details specific to the AC-119G and K models, and are available as PDF documents below.

Foreword by Richard K.Kohn; Chief, Office of Air Force History (76kb)
Preface: Jack S. Ballard, Author (164 kb)
Chapter I: Origin and Early Development (27 pages, 3.3MB)
Chapter V: Gunship III: AC-119G/K (45 pages, 3.3MB)

A substantially shorter (and unofficial) description of the AC-119G gunship and the role of the 71st Special Operations Squadron is available here.

71st SOS Main Page