Rob N:
"When did IH switch over from Cast Iron Axles housings on their tractors to the aluminum ones? Are they interchangeable? I assume the CI ones are more durable?
I believe the switch from cast iron rear axle housings to aluminum occurred in the Quietline Series. In checking the Parts Manuals, there is no distinction between CI or Aluminum. Nor do I see any serial number breaks for either. Thus, they would be interchangeable.
I would speculate, that the CI housings would be more durable than aluminum. My guess why IH went to aluminum would be, cost and/or weight.