Marty,
Here is the brief explanation in JC's Tech Article:
"After the 1953 introductory year, it was discovered, the weight of the tire and mount could cause bed side and front bed panel separation (metal fatigue) on rough terrain. Therefore, in 1954 with the introduction of a redesigned stepbed, a small factory bracket was included with the spare tire option. This better held the left front of the bed side to the front bed panel."
