I don't have any real RR experience, as you know. I think that we can look back at the change over to AC units as a big deal. I compare it to the original dismissal of diesel units from the steam era. There were RRs that seemed to deny any benefits of using or switching over to AC units. I can only get an idea of what really happened thru reading what's out there.
It sounded like CN and NS, were two of these big RRs that refused to accept the new tech? I have to imagine there were more including smaller roads. Like the time when steam was the tech, I'm guessing some RRs didn't wish or have the ability to switch over as their assets were tied to what they already owned and ran?
So to me, the end of the SD60(MAC?) production (test units?) and all of the SD70MAC engines marked the new era and I believe should be thought of as important engines in history. I have to reread GE's production. I believe it was their AC4400's that represented their entries? I'm not sure what other model they first offered or tested in AC? I just remember reading of the tests out of the coal river basins using the EMDs. I don't know the full history.
Again I'm just a hobbyist and was not part of any RR.
