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It's a Rural Radiotelephone Fixed Subscriber Unit power supply. Like for farms and so forth. From the MTS days, about 1962. It ran a high band T-Power drawer with 1 or 2 MTS Bell System channels and later a 35 Watt class Motrac.
There was a telephone style control unit that ran the setup, and if memory serves a car battery to (briefly) back-up the setup if AC were lost.
One of the T-Power manuals shows it, just can't recall which one. The manual title says something like "Mobile and Fixed Subscriber..." You can see how Motorola was always good at re-using existing production parts.