1091, 1092, 1093 were bought by the ARR in Fall 2000 from Canadian National Railways. I don't know the exact CN road numbers. (Cabooses are called 'Vans' on the CN). CN's Point St. Charles shop in Montreal built (actually re-built ?) a total of 548 cabooses from the frames of 40 foot boxcars (CN series 472000) between 1970 and 1977. They were based on similar vans on the CN that had been built by Hawker-Siddeley in the 1960's.
I'm guessing, but I believe that the three cars the ARR got were part of CN series 78100-78129. These cars were again rebuilt by the CN in the early 1980's for international service into the USA. These cars were modified at that time to US FRA standards, so it makes sense that the ARR would have preferred those, if they were available.
The three cars were sent to CEECO in Tacoma for refurbishing/painting before being sent to Alaska. (Of course CEECO could have upgraded them to FRA standards if they weren't from the above series). They went to Alaska in Fall of 2000. -- commentary by Don Marenzi