Largest..during the 70s I had three Impalas that had the 5.7L V8. The smallest was a 2.5 I4 (known as the Iron Duke) in a 1990 Grand Am. Never had engine problems with any of them. Point of interest...a lot of these engines are still out there delivering your mail.
Your choice of Mopar or Pontiac 400 cubic inches? My Mom had a 72 Dodge Polara 2 door with the 400 4barrel. Car ran but my 72 Grand Prix with the 400 4barrel would have smoked it. My Grandmother had a 71 Dodge Polara 2 door with the 440 motor in it. Was sold/replaced before I got to drive it. I remember my Uncle Keith & I would take rides on the highway & he buried the speedo once or twice.