Series/parallel between two single coil pickups works better when the coils are of roughly equal output.
With series linking of a P into a J, things could get muddy.
Reconfiguring the output conductors of a P pickup to allow series/parallel interconnection of its coils could prove useful. Parallel mode P is a pretty nice match for the J.
WARNING - Reconfiguring a brand new SPB-3 to four conductor + shield output cable will invalidate your warranty.
OP asked for opinions. That is what I offered.