Fletcher's Granite has at least two wooden B&M cabooses, one is at the Westford quarry and is used as an office for quarry workers. It's interior is completely stripped out so the cupola basically just makes a nice skylight. The other that I know of is a monitor-top at the Milford NH quarry, it's used for storage. Neither are visible from any public roads, and both had their trucks removed.
The Westford quarry still runs a GE centercab to push some steam-era flat cars that haul granite. The 410 in Lowell was formerly used for that purpose when the B&M leased it to the quarry, so I wouldn't be surprised if a number of the cars and maybe even the centercab were owned by the B&M at one point.