As you know Keith, a rhd Lincoln Zephyr V-12 was installed in a F60H and demo'd, as Ford's answer to the requirement for more power in the 6-wheel chassis class. Ford also offered a 'F60X' but the DND elected for a GM version insyead with the 270 GMC unit although it was acknowledged that it too lacked power. I have never seen anything though about the Chrysler straight-eight C60X. That would have been a possible answer to the lack of power question!
I found this link which is interesting. I had forgotten about the mighty GMC V-12 diesel. It rather sounds like a diesel loco engine.
http://uk.youtube.com/watch?v=puJaDf...eature=related