I'm not sure about the datest on when the 1st design transitioned to the second. My guess is somewhere near 1975, but it could be 1971- just don't have enough data to be sure.
As for rust on the lip, I've only posted the one pic which was txt to me. Have not seen it in person.
I've been meaning to post something on the difference, but I'm not near any of my wheels right now to measure the critical areas. Maybe you can see it here:
