Upgrade? HOW DARE YOU!!!
But seriously, don't touch a thing on that beautiful work of art! If the pickups are microphonic or something, just have them repotted. Appreciate that bass for what it is and don't try to make it something it's not and will never be, and you will be rewarded with unique and cool tones.
+1!
The fun of that bass will lie in the fact that it is unique in look and sound. I always wanted to do a gig where everyone played some of these late sixties Japanese instruments. Just because.