From my research, only 2,500 ENDT 673's made it into the trucks. That figure may be wrong but in either case, a Mack is rare. I contemplated selling a truck with an NHC-250 Cummins in order to purchase an awesome cargo truck with a Mack engine. My primary issue, I use my hardly sought after 14 liter N/A Cummins to haul roughly 55,000 pounds from time to time and it does it just fine. It has better numbers than the Mack in stock form and when turned up, it becomes much better. Old school guys say there is no replacement for displacement. Very old school line of thought but it works for me currently. I know of a Mack powered M52A1 not far from here but I'm not going to add it to my list of trucks to pursue either. I do know a Mack enthusiast and even he is not interested in a site unseen, unknown private owner truck. One issue with the Mack engine is it has a flat tappet style cam and lifter arrangement. It makes more power than a multifuel powered truck but parts availability becomes an issue. My friend who is a Mack enthusiast has sold most of his old iron and is looking around for Cummins powered trucks as well. No, I'm not trying to start a fight, I've just been around here for a while and I'm honest.