Car Number versus Serial Number versus Engine Number

Unknown

I have a number of super six's (J, M, O) and I'm trying to understand the literature where a "serial number" is listed. The serial numbers seem to be broken out by body style which means the number on the serial number plate on the car and frame horn is the serial number in the literature. So are the engine numbers distinguishing the year or make of the car? I notice very subtle changes to the engines between the J, M, O in the areas of the water pump insert sleeve and the flywheel weight as well as the cross over air tube and intake. This question is about the engine numbers relative to literature - were engine numbers tracked separately from car numbers? Thanks.