The neck and bridge pickups generally only differ in the cable length to the control cavity.
If the bass has been upgraded, and it has the SC-1 pickups, then the neck and bridge pickup CANNOT be interchanged, because while they are essentially the same, when they are added to the components for the high frequency noise cancelling, they have specific positional roles.
You can use AXY pickups or FatBoy pickups in a Series I/II by turning off the humcancelling trimpots. They will not sound the same as the SC-1 pickups and the HX, but it certainly will function.