So far, it sounds like questionable results for an EFI motor. This is a couple nickels, especially if you have twins, for what may be nothing more than a weight savings. Hopefully, some others will reply with more info, good or bad.

We have installed Imco, Eddie Marine, and Stellings headers, and cast alminum on 502 EFI motors. We have not had any negative feed back from any of our customers. On the Stelling headers, we did install a different fuel pressure regulator to compensate for lean conditions.