Yeah no magnesium in Doc engines.
Doc and FIFI both run engines that have been specifically configured for them, based on available parts. IIRC, the engines are assembled with the turbo-superchargers removed, only the mechanical supercharger components remain in use. Those two aircraft don’t need to reach the same altitudes as when in service, so it makes sense to ditch those heat sources. The Cavanaugh Flight Museum had info about it on the website, back when FiFi was being repowered (over ten years ago now). The museum was involved with raising the funds for the new engines.
IIRC, the crankcases on VW bugs were magnesium?