the 55 2nd series to 59 cabs are identical, doubt there's been any switching on the one you picture, looks pretty unmolested original as far as sheet metal, might have different drive line .... the frame should have the same number as the door tag, minus the leading model indicator, stamped on top of the frame rail near the steering box, like
this 56 .... engine [and other component] number locations are shown in that GM info booklet I linked above, they're not "numbers matching", but will have date codes
Bill
