It can be difficult to identify the model year of custom trucks, because elements have often been changed. A few guidelines:
1948-1950 F-1 Trucks
Most '48 F-1s had a painted background behind five chrome grille bars. On late '48s, '49s and 50s the bars were painted silver.
An F-1 designation was located on the cowl, between the hood and the door.
1951-1952 F-1 Trucks
Grille and fender fronts were changed significantly in '51 and '52. Headlights were set further apart and the grille opening was extended to nearly the full width of the front. V-8 equipped pickups sported an emblem just below the hood.
Base model trucks had a spear-like molding on the hood -- stamped FORD at one end and F-1 at the other. Five Star trim added a bullet-shaped piece at the front of the molding and additional trim above and below it.
The cowl's F-1 emblem was dropped in '52, replaced by a round emblem on the side of the hood. A V-8 emblem was used on the grille.