I think you will get fairly close with the air suspension turned off, but when it brings it back up to level once you turn it back on, it will change things. It will level the truck and partially unload your w/d bars. If the front is self leveling, which I think it might be on your truck, I think final verification at a scale will be required. If the front is not self leveling, then you can let it re-level the rear and then check to see if the front end still has enough load on it by checking height. Does your manual say anything about how much weight you want on the front end? Should you put back 50%, 75%, or 100% of what was removed? You need to know that as well.