Here is a parts system developed for S Scale (1/64th) truck models allowing for interchangeable parts and rapid expansion of the line with fewer pieces.
For a more thorough series of webpages showing the design to product stages on an earlier model, follow this link.

The fender brackets attach on top of the front frame piece inset, so the floor section is level with top of the rear frame.
The hood piece fits between the fenders and rests level. the bumper cut out key is in front. 

The White Motors Super Power hood is more tapered, so it required a particular frame bracket and grille.

Short and extended hoods are interchangeable with the other fender brackets

Grilles fit on the front of the hood

White day cab and sleeper, and Autocar day cab and sleeper-all cabs match up to all hoods.

5 rear frame lengths plus and extension for longer western frames and dromedary tractors. Ruler is scaled in mm, alternating colors 5mm increments, blue square marks 100 mm

Front bumpers

assembly from bottom

Assembly side and top

White Super Power hood models

Short hood assemblies

Extended hood assemblies

Assorted assembles