Have the box on the rear loaded with what you would like to haul. Get a tongue weight with the cement still loaded so you know what it is to start with. Then take the cement out of the front and see what the new tongue weight is remembering there has to be tongue with. If the tongue weight is still positive, go take it for a tow and see how it feels. You may need to put some of it back, but I find it hard to believe it would need 600# plus the weight of the storage compartment that had to be rather heavy/strongly built to hold the cement.
Bill
