Re: a combination of the most interesting sort
I think that would sound great, actually. I've had a Phat Cat (approximately a P-90) in the bridge and a Strat pup in my Strat, and loved the results -- and I'd imagine that a Jazzmaster pup, being more similar to a P-90 (short and wide), would sound even closer. Dang, now I wanna try that... lol
Anyway, one thing to keep in mind, is that Fender- and Gibson-style pups are out of phase with each other, so you might want to re-orient the magnets on one. It's easy on a P-90, which has two magnets with the same polarity facing the poles -- just spin them 180 degrees around the vertical axis so that the other polarity faces the poles. Be careful, and don't blame me if you break a wire or anything.