the 55 thru 59 cabs are identical other than possible variations over the weeks, months, years at any of the different plants they were assembled, any door or front sheet metal from one truck is not guaranteed to fit a different cab, even of the same year - also the firewall stamping was changed slightly for 58/9 with a change in the throttle pedal/linkage arrangement and hood hinge style
the primary difference in the 5-7 and 8-9 is that the later frame is a couple inches longer to accomodate the different fender shape and splash pan below the grill, and the hood hinge mount holes in the firewall are slightly different ... putting the earlier front sheet metal on the later frame requires
cutting the frame horns and redrilling the bumper mount holes, switching either way may require fiddling the hood hinge holes to match the firewall
either way can be done, but will involve some adjustments and a bit of bodywork skill ... the pic of the marked frame above is a truck with a 56 cab, a 57 hood, 57 GMC front fenders and doors on a 58 frame - assembled from parts of
9 different trucksBill
