The extra compressor is for an aftermarket under dash air conditioner. One of my first paying jobs back in the early 1960s was the inside guy on the installation of the Mark IV add on air systems that Dad's shop sold. I would hang the evaporator under the dash and route the wiring, while a more experienced guy did the under hood work- - - -compressor, condenser, lines, control valves, etc. We would start on a job when the shop opened in the morning, and drive to lunch in an air conditioned car- - - - -come back, and install another one in the afternoon! I was 14 years old at the time.
Jerry