731 Heavy Duty

[Bog]

Hi guys my 731 says Heavy Duty on the side under the blue rectangle. Most of the pictures I Google of the 731 say heavy duty. Is there a difference between a heavy duty than a standard 731. Or was heavy duty just a decal used certain years? I can't find the heavy duty decal in the parts book. The only decals it shows is the blue rectangle and the word hydrostatic and the number 731.