Nathan - This shim won't work in the case of the 1951 rear suspension. Our axles are mounted above the spring, where the Task Force truck axles are mounted below the spring. If you added this spacer between axle and spring you would just lower that side even more.
You could add a "lowering block" on the passenger side to try and even out your lean, guessing it won't cause your rear to then be lower than front end, which may not be the effect you are looking for.
