RWRP stands for reverse wound reverse polarity. It's the same thing as with stock Jazz pickups: when both are on they act as a humbucker.
I'm sure any pickup maker could make one for you or (maybe even better) a complete set of pickups. Not sure if they are available commercially since the original '51 P basses are single pickup instruments.
The bass is wired: master volume, master tone and a 3-way pickup selector switch. When both pickups are on they are in series.
Thank you. I’m not much of a gear head in as much as I know how to drive them, but not necessarily what makes them work.