High Mileage Magnum

At 165,000 my 5.9 runs like the day I bought it with 31,000.

I've used Valvoline "high mileage" syn blend almost exclusively and only change every 10K miles.

I do haul loads in excess of the rated capacity, and trailer cars (sometimes full of parts) across the state, plus engage in "spirited" driving from time to time.

I would not hesitate a bit about dropping a 150K Magnum take out motor right into a car with only the fitment issue changes, provided you were able to see it run or was from a verifiable source.