I'm sitting here with my 1995 SB320 on my lap.
I was at work when I replied earlier and relying on memory. Bad idea.
I thought that the main differences between it and yours were entirely to do with that battery cover/holder and the serial number.
In fact, I've just realised that you seem to have an ebony board on there whereas mine is rosewood, and your bridge is completely different from mine.
http://s1128.photobucket.com/user/h4ppyjack/library/Basses%20CURRENT/SGC%20Nanyo%20Bass%20Collection%20SB320
Yours having been bought new it can't have been modified, so I'm even more intrigued than before.
Now would probably be a good time to remind everyone that, despite starting this topic (back in 2006 on a different forum ... eek!), I'm not actually an internationally-renowned expert on the subject, I'm just another enthusiast for the brand.
Think I'll take a back seat and wait for someone else to contribute.
Lovely looking bass, by the way. Do you recall how much you paid for it in 1986?