ALL MB's both gasoline and diesel have sodium filled, self-rotating valves going back to 1973 at least.... And regarding cylinder head swap - just compare head gaskets for each at the dealership parts counter. If head bolts, oil and coolant passages line up then go for it, says me.

And definitely skip the turbo and treat it like an NA longblock if you want to follow the path of least resistance. Turbo's are over-rated anyhow. Either the car will do 90mph or it wont, acceleration is NOT the critical factor. And how many long steep hills do you have to climb in Texas? I think its an American 'hotwheels generation' phenomenon where everybody gets all goo-goo/gaa-gaa over having a TURBOCHARGED engine.