Jim Meyer Racing has built the last 2 chassis' for me. On his design he used 1" upper & 1.25 lower. But he used mild steel DOM rather than chromoly. I have been told not to use chromoly on the street for building chasiss for a few reasons, but not sure on control arms. This is a little out of my league as to the true reasons not to. That's why I leave it to the people that know when it comes down to stuff like this!