Trucks have been discussed, but is it possible to know whether an SP B-50-15 had been rebuilt to steel sides or received a new roof or other equipment?
Specifically, SP 31802 was interchanged onto the Suncook Valley RR on 11/24/1952, with an inbound load of lumber from Gurdon, AR, most probably destined to Emerson Manufacturing, a furniture manufacturer located in an old cotton mill in Suncook, NH. The empty car was returned to the B&M at Concord, NH four days later.
The SP Car Ledger shows that SP 31802 received steel sides in 1950. By that time, it had also received AB brakes, a geared handbrake, and U-section trucks.