If Deaver won't work with you in So. Cal., try Atlas Spring in City of Industry. They are off of Valley Blvd, and Fourth (I believe). They have been around for a very long time (like second or third generation same family), are highly respected, and do all kinds of spring work from trailers to semis. I have used them to re-arch vintage trailer springs, and I have seen lots of 4 by 4 lifted springs. This is a much busier shop than Deaver. It's a full service shop that can do anything requested to manufacture a custom leaf spring. Ask for Fernando (the owner) for advice and questions.