In my opinion, a quality gasket match and polish job could give you some benefit. I would be very, very leery about allowing someone to port my diesel heads. There are a large number of people who are competent to do this same work on a naturally aspirated, spark ignition engine, but not very many who know how to do it for a compression ignition boosted one. They are two different animals, especially when turbochargers are the method of boost.
Making sure all the ports match very closely to create smooth transitions, and that the gaskets have been trimmed to match those same openings, as well as a mild polish to remove casting lines and rough texture is as far as I would be willing to go in an engine that would be used for an on-road application.