Have spawned this mob 7 times. Confirm location as posted above. He spawned 3 times in the south square room as the roaming mob, 3 times as the roaming mob in the west square room, and once as the roaming mob in the main square room. He dropped 5 dedicant cores and 2 purification. No sign of shield.
He popped for me in the 3 square rooms just east of the cavern that Ironhorn/Slavemaster can spawn in. There are 2 little rooms connected to a slightly bigger square room. He was in the western room.