From this site:
http://www.public.asu.edu/~grover/willys/id.html
Key features that changed over the years:
* grill - From 1946 until 1949 the grill was relatively flat (See B1, A6); in April 1950 it changed to a sharper peak in the center. (F1, F3)
* grill bars - Before 1950 there were no horizontal bars on the grills (E6); from 1950 to 1953 there were five horizontal bars (D1) with chrome trim on some vehicles; in 1954 the number of bars were reduced to three counting the horizontal ribs forming the top and bottom of the grill(See B5, B6); in 1956 the three bars were not evenly spaced, but had one at the top, one at the bottom and one between but near the top (See B4) After 56, the grill returned to the same configuration as before 1956, three bars (F3).
* hood - From 1946 until 1949 the hood had a rib along its centerline, but no hood ornament (E6); in 1950 the rib was replace by a hood ornament.(F3)
* front fenders - From 1946 until 1949 the front fenders were flat on top and flat on the front (B8); in 1950 they changed to have a slightly rounded top and a peak at the front (B6, E4).
* bumpers - The trucks always had a plain curved front bumper, sometimes painted and sometimes chromed (D1, B4). The wagons sometimes had the plain bumper and sometimes had loops across the top.(D9, F9) The loops were optional. I don't know when the loops first appeared, but they may have been discontinued after a few years, as I haven't seen any loops in later years.
* rear pickup window - From 1947 until 1952 the pickups had a small rear window (E6, F1); the window got larger in 1953.(D4, F3)
* steps on pickup - Behind the cab, in front of the rear fenders, the pickups had steps from 1947 until 1949.(A6, B8)
* windshield - The early years had two piece windshields (A10, A11). In 1959, Willys came out with a special "Maverick" model which had a one piece windshield and the roof was flattened slighly to fit (E5). All wagons and pickup trucks went to the one piece windshield in the middle of the next year. There are some 1960 Willys with two-piece windshields and some with one-piece. All vehicles produced in 1961 and later have the one piece windshield. (D4)
* gauges - From 1946 until 1949 the gauges were rectangular (F4, E6, D14), after that the speedometers were round with small square gauges across the bottom. (D6, D13) Later, there was a larger round speedometer with the other gauges incorporated into it. See pictures of all three.
* pickup tailgates - From 1946 until 1953 these vehicles were produce by Willys Overland Motor Company, and the pickups had the WO logo (that is a watermark on this web page) stamped in the center of the tailgate (E6, D13). In 1953 Kaiser purchased the company and it became the Willys Motor Company division of Kaiser. The WO logo was abandoned, and pickup trucks had "WILLYS" stenciled in the center and "4 Wheel Drive" at the right side (on trucks of that type). (D18) The "WILLYS" was replaced by "Jeep" later. I'm not sure of the exact year, but a 1960 owner's manual shows "Jeep". Chris's has been repainted (D4), but Landon's tailgate looks original. (A20)
