A friend of one drove a one ton Ford (dually) utility truck with the 7.3 engine and standard transmission. Think he put well over 300,000 miles on it, before he retired.
No problems that I recall. He was very high on it. The Ford 7.3 liter diesel V8 was an engine made by International Trucks (Navistar)....for Ford.
The only problem I can see is that all of the 7.3's are fairly old now, haven't been made for a long time. But if it's ...as you indicated...low mileage, well maintained, owned by someone you know and the price is right...I would say seriously consider it.