@Scottl the later version with the side ladders (plmx and cbtx in this release) is the most common version I see at work today, I see both of those schemes and if you can find the older Procor and utlx releases they are spot on... The other version with the platform across the top are still found but they are becoming less and less common, I have seen lots in the last 8 years tho.
Not sure these would push back into the 1970s they have the modern insulation jacket that dates them to the 80s +
N scale definitly needs an earlier version without the modern features.
Edit: in a Halcon cab on my way to work and blocked by a train in Edmonton, saw both PLMX and CBTX cars (identical to this release) and a older version (same as athearn) in UTLX.
CP not CN but we both serve so many of the same customers you would see them on CN too.