Reference post 18: the air cleaner used was not completely consistent between Mack and Continental engines. If one was damaged in the field whatever the parts man had would be put on the truck. The Army had kits to convert gas engine trucks to either Continental or Mack engines which would require a new air filter as the gas engine's was under the hood. If an engine was replaced in the field apples went to apples and oranges to oranges. It would be difficult to replace a Mack with a Continental engine as the starter, air pump, fuel pump and alternator would be on opposite sides of the engine. I sure someone will tell be it was done somewhere but it would require a lot of hours to change all that over.