So here's my review for the Ibanez Mastercraft GS-15 from 1980:
This guitar is heavy built, much like the Kohno and Sakurai guitars from the same era. In fact it's built exactly like a Kohno from the 70s, the only thing that differs between the GS-15 and a Kohno No.30 is the rosette and the purflings. It has solid spruce top, and solid Brazilian rosewood back and sides, even the tuners are the same, as well as the headstock, double reinforcement ebony strips and of course the internal bracing. No cracks or repairs, the action is good, with much remaining saddle.
The neck is on the thick side, which gives a very solid sustain. The sound is deep, yet clear, with round and warm trebles, even on the high notes. The midrange is somewhat pronounced. Scale is 650 mm and the nut is 52 mm, which makes this guitar more accessible than the older Kohno's. So what we have here is basically a late 70s Masaru Kohno No.30 (or earlier No.20 with Brazilian rosewood) with 650 scale, nothing more, nothing less. So if this is what you are into, it doesn't get any better than this.
Due to the heavy build and quite thick neck I guess this guitar won't see that much play from me personally, but it's still a very nice and extremely rare guitar. However, I'm seriously considering givning the neck a new slimmer profile and the top French polish. We'll se about that...