Hi Kydd.
As you have suggested, your 12 string was built in the late 1960's by Kawai. It is modeled after a Burns Bison although the headstock shape is pure Japanese. Turns out your guitar is pictured in the book Bizarre Guitars of the 60's but the description is in Japanese so not of much help to me.
I don't know what it is worth, maybe someone else has shopped for a guitar like this recently.
Here's the picture from Bizarre Guitars in case you would like to see what the missing ashtray/bridge cover looked like.
