Most of the Tokai pedals appear to be clones of popular Boss designs of the time (for example, the TFL is a clone of the Boss BF2) so it's probably safe to assume that the distortion will be along those same lines, probably a boss ds1, although I can't find any schematics to compare them. As you know the Tokais were made in Japan so would have used the same high quality components as the older Boss units, which are held in higher regard than the modern models made in Taiwan.
Make sure you get one with a metal enclosure. The ones with model numbers ending in "2" were plastic, "1's" were metal.