I am only reciting that research path here to say that "No, I really don't have a very decent wish list" to refine what I have, and perhaps my meanderings will result in someone suggesting something better.
The existing index is optimized for searches of the names of individuals. For the particulars of this general matter, I have been quite lucky in having four non-common family names which are pretty precise in yielding a restricted set of 'items'. Now, as I learned, there are basically two sets of microfilm rolls that Secy Mo has indexed. They divide the universe into matters pertaining to an individual and matters pertaining to more than one individual. With regard to the series pertaining to an individual [300 rolls], the next level of compartmentalization is an alphebetic range. From that I ended up ordering four rolls, and the results were pretty satisfactory. When, as it turned out, however, that there was crucial evidence concerning more than one person, I messed up, and did not end up with the right section of papers [94 rolls]. In the 'group' compartmentalization, the next level down is really a break by geography, and I ended up with a lot of really interesting facts about events in Baltimore, and none in St. Louis.
Now, in the 48-hours since the folks on this forum have been so helpful in suggesting other sources and alternate ideas, I have revisited the Secy Mo index and tried to coerce it into yielding a good set of items based either on the class of 'disloyal activity' [assessments, General Orders, etc.] or on the name of one of the Provost Marshals or Board of Assessment Members. All of those searches seem to result in the need to pull/view more than a dozen different rolls which is a little prohibitive in my remote-access case AND [to finally get to the point] an unfair thing to ask of your forthcoming visit to the sources. That said, and apologizing in advance if this turns out to be a nightmare for you, below are the cut-n-paste results of two queries that resolve to only two different Reel Numbers: F1238 and F1404.
Churchill, Samuel B.; McPheeters; Garnier; etc. Saint Louis St. Louis Protest against General Order 24, the tax assessment levied on friends of the enemy to aid refugee families driven by the rebels from southern Missouri 12-26-1861 F1238
Thomas, James S. Saint Louis Appears to be last page of letter from Thomas. Letter refers to Rev. Elliott's petition of remonstrance. Notes that the petition was taken to Gen. Halleck in Washington and, with the support of Governor Gamble, the assessment was suspended. N. D. F1404
Thomas, James S. Saint Louis St. Louis Letter from Thomas asking Brig. Gen. Schofield to answer questions regarding the issuance of Special Order 91. For example, he asks if it was ordered under the authority of Gov. Gamble. Regarding the powers of the Board of Assessment under the order. 12-03-1862 F1404
I am not sure, but I think that Reel F1404 will turn out to be one of those from the 'single person' category, and therefore sequential search within the reel will not be bad -- they are close to being in alphabetic order -- taking into account alternate and mis-spelled names. The first one, however, is more apt to be from the 'more than one person' category, and I am not sure about the sequential ordering; let's hope it is by date.
Thank you every much for whatever you may be able to locate. Please don't spend more than 15-20 minutes looking for these items for me. If you are able to download jpeg images of anything that seems relevant, those work better for me than fiddling with optical adjustments, contrast, focus, et. al. and trying to get a decent printout of what is often a rather poor image.
I hope that you are successful on your own search for materials on your visit.