It was common for Chevrolet to install large armature starters on vehicles equipped with the 168 tooth flywheels/flexplates since they were considered heavier duty. The larger armature was a bigger starter motor basically, and a little longer, that has a short copper tube connecting the solenoid to the field of the starter. The copper tube(dead give-away for large armature) is about 1/2"-3/4" long and this is about how much longer these starters are than the standard armature starters used in engines with the smaller 153 tooth flywheels/flexplates.
