It's called the Duck Walk.He's still touring, so I can't imagine going back in to the studio would be that taxing in comparison. I saw him about a year ago, his voice doesn't sound that different at all, his guitar was a out of tune, but from what I've heard in documentary series, that's apparently nothing new for his live performances. Hell, he even did the hop/skip thing he used to do that Angus Young ripped off. So it seems like re-records would be totally doable.
Either way, you'd think there'd be some more recent live recordings that would be useable, like the soundtrack to "Hail! Hail! Rock 'n' Roll".