Though the 1955-1959 GM doors are basically the same and will interchange, there is one noticeable difference. The inside metal door panel (covering window and door mechanisms) is held in place with smaller screws in 1955.

It is assumed these smaller 10 x 24 screws were easier to break or strip when over tightening on the assembly line. By 1956, GM had increased their size to 1/4" x 20 and this remained through the series.