Guess what I found? A 1979 El Degas Les Paul!
http://best-vintage-guitars.de/el_degas ... _860W.html
According to this site, the guitar was a product of Chushin Gakki (Gakki simply means "Musical Instrument" or Musical Instrument Company"). Chushin has a long and well respected history of instrument making, similar to Matsumoku. They were established in 1948 and apparently closed around 2012.
This site appears to be run by professional guitar luthiers and they seem to have done their due diligence on the items for sale, so I tend to believe them. This would then make my theory (my hope really) that Matsumoku was the builder to be invalid. And the more I think about it, the more it makes sense.
Here's a translation of the description, or you can bring up the page in Chrome and click on the "translate" option:
The pictures of this restored guitar are just drop dead gorgeous, as are all the instruments on this site.El Degas belonged to a New York music distribution company and was one of the better known brands under the many copies due to its long-standing market presence. This cool item comes in the creamy Vintage White and was the top of the line model of the El Degas range. Full-bodied and equipped with the most elaborate design features, in the style of the US model. This LP plays loose on the same level as an old Tokai, Greco, Burny, etc.
Built in 1979 by Chushin Gakki.
Mahogany body
Maple top
Mahogany neck, medium C profile
US style Trussrod
Rosewood fingerboard with cellulose inlays
Fret Edge Binding
Brass saddle; Width: 44 mm
Bünde & Sattel freshly dressed, strings: 1,5 mm
Tune-O-Matic bridge with brass strings and fixing directly in the wood
Maxon pickup
High quality electronics
Weight: 4.40 kg
Interesting huh? Maybe we finally have an answer?