Today, dollar for dollar, is the 318 faster than the 340 ???

He may not have meant anything by it. Nash Rambler and Hudson merged in the fifties to try and survive because both were getting beat by the big 3 automakers. Nash and Hudson "sort of" dropped their names and went with AMC. I say sort of because my '64 title still says "Nash" on it. Remember the Hudson Hornets? AMC Hornets? Rambler to some become a trademark name that stemmed from Nash. Because Nash Rambler was a given. Can't say what the guy meant, but maybe he was just using the trademark name.
Oh he meant something by it! He was snickering and laughing and even when I would correct him he would say it again and Snicker and laugh...