My friend has a brand new S&S engine in a crate, about the same era, an Evo style mount, I think it's also a 1989 Classic he got it for.
Are you gonna pull the jugs and look at the primary, while it's out? That many miles and I suppose since it's out, I would just replace all the gaskets/seals, and this would allow you to see what's worn-out and ready for replacement.
I think Gramps would ride it for a bit, and then say, "thanks," and hand you the keys.