Torque boxes are a good thing to have on all four corners. I don't think boxed lower arms are needed on a strait line car though. Mabby if it was a road race hadeling car then I would see boxing them for that but I don't think there could be a lot of load on them just going in a strait line. But that is ust me. You coud put a pinion snubber on too but a lot of the time a car with S/S springs does not need them because S/S springs make the rear of the car rise making the snubber usless as it will not hit the floor. I would go to the track and see how the car does before deciding if you need one or not.