Hi, nice instrument. Interesting that it says Gibson on the headstock; also interesting fretboard markers.
If it were me, I’d look into getting that pickup rewound. Well, first I’d do some research (if you don’t already know) on which make/model/year the bass is, and in particular, what people think of the pickup in that bass. Or just use your own opinion of "it sounded quite good" — that’s what has me thinking to get it rewound. Plus, you know it will fit perfectly.
Alternatively, I’d look for a likely drop-in pickup solution like the Artec PU-EBA (there are other possibilities too, that’s just the first lower cost one that comes to mind) to preserve the look. Oh yeah, there’s a newer possibility called the
Retrovibe HotMud, about which I mainly know its cover looks like a mudbucker/sidewinder, it’s ohm rating is like one too and the price is right. Carefully check the dimensions before proceeding, though. Similarly, for a bit less dramatic sound but still in the same vein, you could look for a used Epiphone EB-0 or EB-3 pickup. But, your own pickup cavity’s dimensions might not be Gibson standard though, so you might check on that or measure.
Beyond that, well you’re clearly ready to experiment, and I can understand that. For me, I’d probably want to preserve a classic look and put any second pickup by the bridge. Other people will know better than me, but IIRC, the modern SG bass and the EB-3 use slightly different bridge pickup positions, so I’d get some opinions on the pluses and minuses of each, measure carefully and use one of those two positions.
Finally, I’ve also always been curious about how a pickup would sound in the P-bass sweet spot position. Heck you could even do a three pickup version, with one in the P spot. I probably wouldn’t, but maybe you would
