[DanEC]

In my opinion both are a concern with a steel bolt threaded into an aluminum part. But for most of these cars that haven't been bolted together for 20 or 30 years - galling is probably the biggest concern. In addition to using anti-seize on any bolt into aluminum I have another rule of my own, which is never to remove a sparkplug or other torqued fastener in aluminum on a hot engine. I'm sure people do it all the time and manage to get away with it but I think that is how most plug holes get stripped in aluminum cylinder heads.