Specific to that engine, it would be ideal to have a later head casting. An original casting can have no crack symptoms during the pre-purchase inspection then suddenly there's pressure in the cooling system overnight even if you never overheat it. You just never know. If replacing a cylinder head is enjoyable to you, the 603 is about as enjoyable as it gets. Everything except turbo attachment is well thought out and DIY friendly. The job costs $1000-4000 in parts depending on whether you buy a used or new head and how many while-you're-in-there's you choose to oblige. The bottom end shouldn't need more attention than crank seals ever. Then there's the transmission. 300K miles is a long life for a 722.3. Sure they can last longer. They can also last half that. Next is the car itself. How do you feel about long distance shopping for rust free examples?

Sixto
MB-less