Ken,
Glad you were able to get Bethel's book on RG 109. You will use it a lot. I have Volumes I and IV of the RG 393 PI's. I have used all four at Archives but found most of the records concerning the US organizations that were in NVA were found in the the two volumes I purchased. I couldn't justify buying volumes II and III. I haven't done much research on the Federal units associated with the IT so can't speak to which volumes of RG393 those records might be found. But, I would guess that what records that do exist will be found in Volumes I and IV. (The Kansas records being and example.) All of these NARA PI books are out of print and in most cases, very difficult to find. Abebooks.com is the best place to watch for them. The good news is that there is little demand for them and I think most book dealers don't really know what they are, the net result being that they are usually reasonably priced.
Hugh