I've built a Gecko bass (5-string) with three pickups. The body came routed for two pickups (P2 shape) in their standard bridge and neck positions. I had to use a router with a special jig to carve the middle pickup route between the two. There was very little wood left over (~4mm) between the pickup routes by the time I was finished.
Since the Gecko 6 has even less space for pickups on the body than the Gecko 5, I don't think you would be able to fit three P4-shape pickups in a Gecko 6 body, unless you asked Warmoth for custom pickup positions (add $45 for each route) or do the body routing yourself.
It's a good experiment to try, and for those who need all the tonal flexibility of selecting individual pickups (or even individual coils) there is much to be learned. But most of the time, two well-chosen pickup locations (i.e. customized) can be more useful, depending on your needs.
As far as pickups, from the selections you gave, I prefer the Delano SBC series. They have a lot of usable midrange and brightness in the treble without sacrificing any of the low midrange or bass. The Nordstrands sound more "peaky" and mid-scooped, while the Bartolini "deep tone" series will sound treble-reduced and muffled by comparison.
Most enclosed "soapbar" shape pickups use blades instead of polepieces, and these will work with pretty much any string spacing. Both the Delano SBC and the Bartolini "deep tone" pickups use blades. The Bartolini "deep tone" quad coil pickups actually have a gap between each of the coils, which would be in the dead center of the 6-string pickups. But you probably won't notice because no strings will pass over that point.
The Delano SBC quad-coils are similar (i.e. there is a gap in the coils) but the pickup coils are wired (and magnetized) to effectively work like a regular P offset pickup and a reverse P offset pickup in the same housing. This is in contrast to the Bartolini quad-coils, which are "inline". Tonally, the SBC quad-coils sound pretty much the same as the dual-coil SBC. On the SBC quad-coil pickups, I believe the blades are continuous (i.e. no gap like the Bartolinis) across the entire pickup length.
fretless bass, passive pickups, raw exotic woods
Warmoth Club #51 - Warmoth Gecko Club #2 - Oregon Bassist Club #51
Last edited by tubby.twins : 10-26-2013 at 01:38 AM.