Why it's not Tokai:
It wouldn't be the first time or even unusual that a manufacturer also distributed brands/labels they didn't make themselves, a prominent example was certainly Moridaira/Morris.
So far I could not find any Gaban offer that had some interior pics substantiating any theory, except this one:
http://www.teenarama.jp/gaban
That would be an FLG-650 (set-neck top model) with Maxons from 1974 and there's a lot of pics on that site, here are the most important:
Tuners with Kasuga logo
Plywood top and (interesting) less chaotic routing than seen on many later Kasuga made guitars
What's remarkable is that Tokai seems to offer only a selection of all the Gaban models in that catalog. Besides at least some of the guitars being definitely
not made by Tokai, none of the other guitars would remind of Tokai in any way. Instead, many of them are like "seen that one before with a different label" and the model selection and appointments on them do seem to point much to Kasuga as well.
Why it could be not "not Tokai":
I've put my foot in my mouth about that before - the Sigma electrics do not look distinctively like Tokai either (why would they, they look "era-typical"), but the Sigma plywood SG-copy with the German carve reminded me so much of something else that I claimed this wasn't made by Tokai. Later I found the same guitar with Tokai on the headstock.
So if Tokai made bolt-on plywood planks for Martin, why not for "Gaban"?
But then again - nothing would've kept Tokai from sourcing electrics elsewhere to offer a one-stop solution for Martin and maybe the source was the factory that also made the Gabans ...and maybe they thought "why not offering some of those through our growing retailer network as well?".
In other words this is one of those mysteries again...
Edit: Forgot to mention that Gaban and Ganson are usually treated interchangeably as both labels featured the same models and are both attributed to Kasuga, and that attribution checks out pretty well...
Ganson bolt-on LP copy with 1973 Maxons