Not DPU, but RCS Locotrol. I would say that the 3rd unit is the 3623, slave unit to the control unit 3622, Photo ID: 464690. When these units were first delivered, they had the "hot dog on a stick" antennas, but the range was not good and the slave unit would lose contact with the control unit, so before the end of 1968, the UP put the large "picnic table" antennas on the units.
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