I've also caught the P90 bug. I just made one for a 4 string flying V CBG, P60 maybe? It sounds thick and is
loud as hell. Check Stewmac newsletter archive for a CBG P90 how-to. It's pretty good. BTW an alnico 5
magnet cut in half is a perfect fit up to 4 strings. If you don't want to go DIY Ted's pickups are quite badass.
Would a normal P90 not work? I just bought a couple of mini humbuckers, haven't got anything to install them with yet though, angus young apparently prefers the P90 sound, I'm eyeing off some Jason Loller pickups at the moment, do PUPs need to be custom made because of the 3/4 string thing?