I'm a bit late to the party but...
The serial number on this Aria looks surprisingly similar to the font on the inkies...
Arai/Aria is yet another "factory-less" company that dealt with varying factories. Most of their guitars were certainly made by Matsumoku but if you look into their 1975 catalog you'll find strange cheapo guitars that were made in a, let's say (can of worms), Kawai-ish factory. Dowel tenons were not a Matsumoku thing though (they were the "bolted down tenon" factory).
Adding to the confusion, Kasuga....
Kasugas (at least of that era) have no tenon features visible from the neck PU cavity. The only LP copies known to have dowel tenons are the Fujigen-made Grecos etc. AFAIK.
You don't even have to leave the Nagano prefecture to find more factories that Tokai could've used (in theory), which is one reason why I find it highly unlikely that Tokai set up their own factory. Let me put it this way - "if Tokai had built their own factory in the valley, why don't the guitars look like they were made by Tokai?". That it's just of all the lower-grade models that would have been made in this new factory doesn't make this appear more likely either.
Why would they reinvent the wheel for a guitar like the SS-36, when pretty much all factories that made solid-body guitars at the time produced contemporary (70s style) Fender copies anyway? They were probably all capable of delivering guitars built to whatever specs or grade of refinement you ordered them.
Pic of the neckplate of a 1977 Aria Pro II ST-600 Strat copy. Identical to Greco plates, with "Matsumoku" added.
That Jazz Sound bass this refers to is quite certainly a red herring - the body, or at least the pickguard looks like made before 1976 ("tug bar" holes next to the high strings) and I thought Tokai didn't even make basses in 1977 yet?
It looks like "Matsumoku" embossed neck plates were used quite inconsistently and only 1977 and a few years later, the first (and only) time I've seen that was on "Vorg by Pearl" labeled guitars and basses. But I think meanwhile Fujigen has been more or less sufficiently identified as that "Nagano" factory, right?
Not sure if Reverb.com is still showing the same guitar under this link but this looks like a regular Hamamatsu with the high serial number for 1979 (9008992) and no under the hood pics?
I've always suspected that Japanese/East Asian attitudes towards copying is somehow fundamentally different to those in the west. The amount of care and skill invested in what many in the West would just dismiss as "knockoffs" has always been kind of fascinating to me.
Dismissal by people who wouldn't recognize quality if you'd hit them on the head with it.
I (I think we all here) share that fascination. Re the "attitude towards copying" - understanding that in a broadly generalized way is maybe not necessary or even applicable here, it's basically only a different view on what can be "owned", which is not even that unique to East Asian cultures.
I think the Tokyo High Court sentence in the 2000 "Gibson vs. Fernandes" lawsuit points at something. IIRC it basically says 1. Gibson came 20 years too late with their complaint and 2. that Japanese people are generally smart enough to distinguish between domestic brands making cheap copies of what they consider a
"generic" design and genuine Gibson guitars using that design. (Full translation and interpretation (both utterly confusing though) can be found
here.)
Another factor in this ruling was that e.g. the "genuine" guitars were always immensely popular in Japan, much more than the lookalikes (which is why those came into existence in first place of course) and never crossed interests with Gibson's target audience. However, no Japanese company would've even thought of making actual counterfeit guitars, which is what may distinguish Japan from e.g. China (and of course all the good people in the west putting F-decals and G-overlays on their guitars, then flipping them on eBay).
You surely know how Japanese electric guitars started out, before the Ventures came to Japan there were no actual attempts to fully
copy any foreign designs. I think the "copy war" of the late 60s/early 70s was at least to one half propelled by US and later EU importers asking for cheap lookalikes, but even then there were still Japanese companies trying to establish their own designs with higher quality ambitions, many of them went extinct during the "chain bankruptcy" of 1967/68. I believe that making copies was not at all the initial intention of Japanese guitar makers, and that making cheap knockoff guitars for export (or domestic mail order businesses like Nikkoh) was never considered very honorable and "Japanese". That and the fact that they are indeed very secretive about their trade relations etc. is certainly contributing to the difficulties when trying to research these dark times.
Now fast forward to the "replica war" 10 years later - this should be seen in context: Unlike the previous lookalikes of
contemporary models, these guitars were actually replicating (at that time)
discontinued Fender and Gibson models, and they started doing that in a time
when the vintage craze hadn't even really started yet - so this was maybe not even triggered by an overwhelming demand for such guitars (yet). Apart from the short transition phase when the innards seem still a bit behind the looks in importance, they wanted to replicate the "old" guitars not only as true as possible, they wanted to improve upon them with Japanese perfectionism and honor the original guitars that way, at a time when the companies perceivedly "owning" the designs had changed everything for the worse. I'm fully aware that this may sound like a petty excuse to some people living in a world full of crazy patent trolling and all, but that's (I think) how they really felt about it.
Cue the weird brass shielding plate on early Springys - not quite the full aluminum shield that Fender abandoned in 1968 but something Fender "copied" later on their own '57 reissues, just like the idea to reissue their own old guitars.