Yeah, that engine looks fantastic. How many miles did they say it had? Hard to believe it could look that clean inside, and so awful outside. It must have lived in snow/salt all it's life.
TBH I would just leave the outside alone. I would probably swap out any rusty bolts for ones from your old engine (aluminum bolts have to be replaced anyway). But fucking with magnesium.. sometimes not a great idea. Not only is the dust toxic, but the metal is extremely flammable. And you will never see it anyway.
Funny thing. Aluminum actually oxidizes way worse than steel when exposed to salt. Everyone thinks it doesn't "rust", but it really does (and quicker when conditions are right) - it just doesn't turn red when it does. It turns to a useless white powder
