There are a couple in the 540R that I bought from a pawn shop, recently.
It's only written IBZUSA on the pickup cover but from what I've read at jemsite, it's the same thing, and the measured coil resistance supports that. They're simply wired in hum-cancelling mode with the green wire to the selector switch, the red wire to ground, and the other 2 wires connected together in the pickup cavity.
They sound OK and were a good idea when they were released about 25 years ago but the level drops a lot when switching from the bridge humbucker to one of those. But I'll try replacing them with Virtual 2 pickups which are a more recent model of stacked humbucker that have higher output and lower coil resistance, and are brighter. And since they have less magnetic pull due to their Alnico2 magnets (as opposed to the HS-2's Alnico5), they can be placed closer to the strings for even more output.