
I am often on the westone.info site doing research and finally got around to looking at their listings for Westone acoustic guitars which were made in the 1970's by Matsumoku. And guess what? There are several models there which look suspiciously identical to some of the postings made here by our El Degas forum members!
In particular there are some which sport that unmistakable trapezoidal insert on the back such as on the El Degas M10,
http://www.westone.info/w40.html
http://www.westone.info/w1819.html
http://www.westone.info/mw40.html
and there are a few which show the thin vertical mosaic inlay up the back as well.
http://www.westone.info/mw30.html
http://www.westone.info/mw20.html
http://www.westone.info/w20.html
My GB25 has that feature.
To my eye the head stocks on these are also the same as many of the El Degas posts. However, all the models listed appear to relate mostly to Martin or possibly Fender acoustics, I don't see any based directly on Gibson models such as my GB25 (Dove) or the GB29 (J200 Jumbo).

BUT I have my suspicions that these are also Matsumoku made, just because of the age, the origin, and the quality!.
For those trying to get a better fix on the model your guitar is based on and the possible manufacturer have a look here ('70's and MIJ only):
http://www.westone.info/indexacoustic.html
Happy sleuthing!