From what I initially posted. Looking at a copy of an SAE document below,
it seems to say closed deck block were cast using a medium pressure diecast with sand core, rather than High pressure diecast they used for open deck. Someone on another forum was saying the sand cast process had a duller finish. Though how you would tell that now on a 10 year old block I'm not sure
http://surrealmirage.com/subaru/files/SAE_boxer.pdf