The hood is meant to NOT fit tight against the cab. The Road Boss hood floats over the cab cowl. This was to give the truck a streamlined look and give the appearance of a longer hood.
With that said, install the hinges to the grille, the grille to the hood and the hood to the chassis BEFORE installing the radiator (otherwise you will have a dickens of a time spreading the frame to get the hinge pins in the holes). Then test fit the cab to the hood to line it up. If you install the cab first, then you will never get it lined up right. This goes for the Autocar, Diamond Reo, RB and White-Western Star kits.
Tim