OPERATING ERA: 1944 to 1972. This Kit now comes with our new One-Piece Roof Frame. The Rock Island converted B-2 Box Cars into Stock Cars starting in 1944. The first 200 cars #7700-77199 had a different side slat configuration than the later converted 320 Cars. When the metal roofs wore out, they were removed, leaving the wood under-roof. It is not known how many cars received this treatment.