Jim, You're correct about Betty Wiltshire's work as being the best published source available at the current time on that subject matter. It's too bad you live such a long way from the MDAH.
Mr. Grady Howell would be the only person I can think of that might have additional knowledge. Mr. Howell is such a wonderful open individual who is willingly to talk to anyone from my experience and others who have spoken to him.
I can appreciate your time and effort on such a worthy subject matter. Unfortunately doing research on this subject may take a long time involving years as you stated. Such is the case with raw research but the end result would benefit so many others in years to come.
I do wish you continued success!