I'm sure Tony at Planet Bass would be happy to share the serial number with anyone who asked. We did change from Schallers to Gotohs as the default tuners around 1986 or 1987. I don't recall when we got the custom markings put on them, but probably within a couple of years of the start. I would guess this bass as a 1991. We had an amazing gold plater at the time that was even willing to do the machine screws and not mess them up

The bass looks in great condition, but it's been played a lot - there is some tell-tale wear on the gold plating both on the backplates and the front hardware. That's not a bad thing of course, I'm always glad to see when one of our little babies gets loved!
Pickups are not always indicative of the year - many people still request completely plain pickups on custom builds, so keep in mind the "custom" thing makes guessing hard. Always have to look for several clues.