I just returned home from a research trip in East and Middle Tennessee. I was researching my own family (Dale, Shipley, etc.) but I surprised at how prominent the name Jarnagin was in that region! While I was staying in Jonesborough, TN, I happened to hear a political ad (if I recall correctly) for a Jarnagin who was running for local office there, and then I stumbled upon this reference in the public library there:
Clark, Glenn Susong. 1977. Jarnagin Collections, and allied families. Clark Publications, Indianapolis. 493 p.
I also saw a copy of the same work in the library in Livingston, Overton Co., TN. There were no "Gus's" listed in the index but I only glanced at the volume briefly. It's a massive compilation. You may be aware of it already.
Later in the holiday season, after I get all my research materials from this trip organized and entered, I'll get back to "the band" and I'll be in touch regarding pics, etc.