Two eBay finds: Both Life-Life GP38-2 units. One was Conrail 7940, which has been renumbered to 3976. The other was a Santa Fe, which has been repainted for a patched Penn Central 2107.
Both units are only 2-axle power pickup. Since the layout's turnout frogs are not powered, this can lead to stalls. So these two units are now permanently wired together in parallel to share electrical pickups. Now they are immune to stalls.