All of your observations concerning the distinguishing characteristics of this guitar are right on. The feature that most puzzles me is the Fender style input jack. Japanese builders in this era simply did not use this style of jack, it took time to route and slowed the assembly process. This suggests to me that you have a top of the line instrument from whoever the Japanese builder turns out to be.
As I consider the headstock profile more carefully it is more of a true hofner profile than the teisco check mark profile.
I'm still pondering this instrument.  
