[SS427]

It was very common and still is to this day. I am sure they figured why waste the paint on heavy cast iron as there would be no harm unlike unpainted steel. When you are talking a million cars you can see the savings. Most all the front suspension pieces were never painted for the same reasons. However for some reason that smae thing did not apply on driveshafts. I remember as a kid it was common practice during dealer prep for the body shop to put a quick light spray of black on the rear axle so that car showed well on the lot and hid the surface rust long enough to sell the car.