While lacking in scans of the entire lot (and more pointedly, back scans) the auction listing nonetheless seems to point to 126 as the set length for the small (also called "1955" cards in most guides, vs. 1956 for the "large" cards,even though both sets are from that year). In a ginormous lot that included uncut strips, developing paper and numerous singles, no less than 15 numbers above #96 were listed, including one we can identify as #113 Amelia Earhart as she was mentioned in the listing:
These fifteen cards include three numbers already known and when all the numbers from the lot are checked off the list, reveal 13 numbers still to be identified (although many,many more subjects remain unconfirmed by a scan in the small set). These are: 97, 98, 100, 101,108,109, 111, 117, 119, 120, 122, 124, 125.
Furthermore, by using a little inference, the subset totals can now be determined.
There are eight subsets in Hocus Focus: Airplanes, Baseball Stars, Sports Thrills, World Leaders, World Wonders, Movie Stars, Sports Cars and Westerners. I have been able to confirm that the first five of these have differing totals when you compare the small cards to the large ones. Airplanes, Baseball Stars, Sports Thrills and World Wonders all have five more small cards than large and the World Leaders subset adds ten subjects to the small version. That yields 98 cards over five subsets. The other three subsets, Movie Stars, Sports Cars and Westerners total 28 cards (7, 10 and 11 respectively).
If you add 28 to 98 you get 126 and since that does seem to be the total number of subjects in the small set, those last three subsets remained static in both versions (although I do not know if the numbering within each subset differs between each) and I have marked them with an asterisk in the summary below:
This makes a lot of sense now and I am 99% confident the small set is 126 in length. It's still hard to get back scans of the small cards;I presently have 13 of them, 7 of which are Baseball Stars. Of those, only five are numbers above 96. In contrast, I have back scans of 81 of the large cards.
It's hard to believe that a Topps set from 1955 still has holes in the (two) checklists but that is the case here as Hocus Focus slowly gives up its secrets.