Update on electronics: I plugged two cables into the bass and ran these to two separate amps. This does not produce the stereo effect, as I had hoped. The lower jack produces mono output with all 4 strings sounding whereas the upper jack goes silent when both are plugged into two amps. If you remove one amp, both jack sockets produce mono output.
So, unless there is some kind of special cable to achieve the stereo effect, this bass has been rewired for mono ... and its effectively a P bass alike, albeit a cool old British one!