In May and June of 1978, the American Rail Box Car Company (Railbox) sought a unique design of 77-ton Plate C box cars from FMC. These cars had a 6' plug doors in addition to the regular 10' Youngstown slider. With an original fleet of over 1950 cars, the "Combo Door" ABOX car has since became a classic of Railbox era.

Through October 1984 to July 1985, the Canadian National acquired second-hand nearly 1000 of the original ABOX FMC 5277 Combo Door box cars. These cars were repainted Tucsan Red by CN's Moncton, N.B. shops. Others were pressed into immediate service in original ABOX paint with reporting marks restenciled for CN.

Additionally, the Minnesota Dakota and Western Railway acquired a variant version of the FMC 5277 Combo Door Box Car through SSI leasing. These cars were unique in that they were equipped with EOC cushioning and had eight panels to the right of the 10' sliding Youngstown door. The MDW acquired these cars in November of 1976. These cars were dressed in colorful green and white paint schemes which gave tribute to the lumber industries of the northern Minnesota.