Hey Barrel! Welcome to Mercedesshop!
I would think that your mechanic ought to be able to see any blatant (to him at least) signs of extreme wear or other equally bad items. If he doesn't have precision measuring equipment to check clearances with, I would be that a decent machine shop does. If the body is in that good of a shape, why not rebuild the motor...you're already a big step ahead by having it removed and disassembled...go all the way. (that's what I would do, anyway)
03/83 300D 184k
07/73 280 160k