Hey Fellas,
All good observations concerning the mystery guitar but I am going to stick with my Kay attribution. I think it is basically a Kay Swingmaster with a different tailpiece than the models distributed in the US.
wietse, your observation about the fret markers is accurate, but check out the fret markers on this Swingmaster, they almost go completely across the fretboard. I think we have a match on the headstock, knobs and pups as well.
The tailpiece and the binding are two componets that don't match, but the tailpiece on the Grassi is certainly styled after a Kay tailpiece. I think Grassi was only a distributor so it seems reasonable they may have imported Kay's. They may have also been able to get Kay to built guitars with their choice of hardware. I think it is also possible the tailpiece is not original but I don't have a catalog from every year of this era. It may be just a different model year than my picture.
If it isn't a Kay, it is certainly a "Lawsuit" guitar. If I were Kay I'd sue whoever built it.