https://www.facebook.com/groups/Northwe ... 2328269032
I don't know if the link will work, it is to the private facebook group Northwest Railfans, you may need to register to see the comments (I have posted everything else). Not a lot of definites here (nor grammar). I'm not sure who the owner is but a comment says they were used behind SP&S 700 so I can guess. They were stashed at a business park I worked out of eleven years ago, along I-5 in the south Portland metro area (on a Portland & Western/G&W branch), and apparently out on the old POTB line before that. According to the comments there was a fire in at least one of them.

"Northwest Railfans
Alex Eggleton ·All-star contributor
16h
two pieces of history….all be it from the east coast wait in a siding in tigard,OR waiting there soon to be fait with the scrappers torch"

Hi
The (2) RDC's on the above post, were built for the Boston & Maine Railroad. RDC 6905 & 6911 were RDC-9's the bottom photo shows 6905 in the MBTA paint scheme.
The units were built in 1956,, for the B&M RR, by the Budd,,Pat.

They are non-driving, but motorized, trailers, with 1 engine instead of the 2 in all other kinds of RDCs.