Weight and geometry are two different things. You're comparing apples and steak. Adding spacers multiplies the effect of the weight on the case.I'm thinking it cant be any worse than the weight of a backhoe on the rear.
You may not be pushing it to the breaking point. You not even be near the breaking point. But spaces do absolutely lower your margin and bring the breaking point lower. That may still be nowhere near what you do with your tractor. Or it might bring the breaking point right to the edge of what you normally do.