I speak from experience. Unless you are doing very frequent and long walks for shore dives, why would you worry about a 3/8 inch leg length difference for diving? Once you are in the water, a leg length discrepancy is not going to make any difference, and will not be noticeable. I would think trying to customize your boots, which may also mean two different sized boots and fins, is going to be more of a problem than the leg length. As one who had a slightly greater leg length discrepancy than yours due to an arthritic knee and hip (before I had them replaced), I think your greater problem is how that leg length discrepancy is going to adversely affect the rest of your body in the long term. I waited way too long to get my defective knee replaced, and that delayed decision eventually destroyed my hip, forcing me to have the hip replaced on the same side as the knee, and has also caused problems in other major joints on the other side as well as the spine. Now all is temporarily in balance, but I fear my delayed replacement procedures are eventually going to get me enrolled in the Joint Replacement of the Year Club. I would invest in some good, well designed and fitted orthotics for the shoes that you will wear every day, and just enjoy diving with your current boots and fins.