Yes, it's basically the same as "Kodalith" film that was used in typesetting machines and to make backlighted title cards for movie credits (at least that was what we used it for).
Any Kodak product that starts with "SO" stands for "Special Order".
When Kodak started offering Polyester (Estar) base for motion pictures in the late 1990's, all their polyester based films were "SO - XXX". After a few years, they altered this naming system.
The first number designation from of the (35mm) film was changed from "5" to "2" to denote the new base. Thus, their 5324 Fine Grain Duplicating Panchromatic Negative Film (acetate) was also offered as 2234 Fine Grain Duplicating Panchromatic Negative Film (Estar).
As far as I know, the "SO" designation is still used for custom orders of unique film types or bases.