> but mechanically it probably wouldn't spin up

might not spin up. I recently booted a Sun 3/80 from 1990 and while the battery backed RAM that told it how to boot was long dead, the HD was not a problem at all. Once I replaced and re-coded the RAM, the machine booted right up. And this isn't just a one off story. I've got a bunch of machines from that era, and the HDs are not usually an issue (although occasionally they are).