318 industrial?

does anyone know the the difference between the 318 industrial engine and
the 318 that came in cars and light trucks? these are not the poly motors and thay came in bigger like 2ton trucks, motor homes and farm equipment.
i thought maybe they might have thicker castings, or steel cranks or some thing. the heads are different, and use a different type of plug but not sure on the rest of it. i need to rebuild an engine for my scamp and have one of each, one is out of a 72 motorhome the other is out of 72 satellite wagon.
any info would be appeciated