From 1941 through 1953 the GM pickup bed sides are the same, however, a major design change began in 1954. This new style with very few modifications continued to the end of the true step beds in 1987.
The unique feature of the 1954 through 1955 mid series bed sides is the flowing grooves that fit the edges of the rear fenders. These apparently gave a better seal the older design fenders were bolted to the new 1954 sides. It prevented mud and dust from passing up from the wheel well area.
For the perfectionist: These sides will probably never be reproduced. The expense of tooling for a step bed side that was only used less than 16 months is not practical. Originals will remain the only source for the correct restoration.