55- 59 chevy trucks used the same crossmember. the 55-57 and 58-59 gmc trucks used different crossmembers than the chevy. They are the same for the year groupings I noted. The major difference with the 55-7 and 58-9 xmembers is the radiator is supported by the crossmember on the earlier gmcs, and not on the later ones. Maybe you can find a serial number stamped on the frame to tell you for sure what you have.
