[rverdlm]

The rear of your 450 is bound to sink a few inches when you load 4K pounds on it unless you have an air suspension like on a HDT where it has a leveler device to always maintain the same level regardless of load. You don't need a completely level spot only a spot that is straight. Just measure the hieght from the pavement to the rear of the frame and then from the pavement to the front of the frame.