Ralph,
No. I can't find that mentioned anywhere, CN may have built in-house just like most of NZR stuff was.
The car pictured doesn't have enough overhang outside of the truck sideframes to be a re-trucked s.g. car, since it was a 50ft'r and those auto's are small cars, not much room appears alongside with the upperframe members. I can't find any reference to how these were used in service, i.e. how and where were these loaded/reloaded, trans-shipped? It seems logical that truck swapping might have been/become the answer but s.g. trucks put under that sized car seems implausible, at least to me. I haven't drawn much luck other than this.
Another thing is just how many in that 18000-099 number block were actually in service? That's an awful lot of capacity for NFL.
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