maybe a daft idea, and I've no experience of it, but what about lead, as in lead loading it, like they do for car bodies. Works fine on steel, can't think of any reason why it wouldn't work on alloy. Melting temperatures differences should be safe enough.. build it up, and dress it back with files etc.
might be worth a dig around to see if it's feasible.
might be worth a dig around to see if it's feasible.