GM continued to make replacement engines of the earlier design, so it's entirely possible you have an engine that was not installed in a production line vehicle. The change in the body style in 1955, of both cars and trucks, necessitated a lower water pump position for hood clearance for the fan. The radiator was also lowered and widened in 1955, mid-year for the trucks. Replacement engines with the early block casting continued to be made for several years, however, with some internal changes in machining specifications.
Jerry
