The problem with cheap vintage instruments(and I have been told most all vintage instruments), is that you really need to play the individual one you intend to buy to get a good feel for it. As far as old Japanese stuff, the Matsumoku factory turned out some good stuff.
As far as the oddball original designs that you will find cheap from the 70`s, they are even worse about buying blind. For me, some that look comfortable aren`t, and some that just look meh play great. So I think the best research you can do is with an amp and some time….
Luna Pheonix - First Bass, still a player
Ancient Aria Violin Copy & Kent 70`s Super Short Scale- Projects