/6 Mileage ?
My first brand new car was a 74 AMC Hornet with a 232 6 with a 3 speed manual. My roommate purchased a new 74 Dart Sport with a 225 and automatic.
The AMC got low 20's around town and mid to high 20's on the hiway. This was a time when gas mileage was a very high priority because of the gas crunch that only allowed you to purchase gas on alternating days. Once on my way home from Hartford to Boston I kept it at 55 and drafted semi's any chance I could get and I was able to get the mileage to 30, but that was not something you could expect.
My roommates Dart Sport got about 2-3 mpg less than my AMC which at the time we attributed to the auto tranny.
Also, in the late 70's I purchased a used D100 short bed pick-up with a 225 / 904 combo. This truck got about 12-15 mpg around town and 17-19 on the hiway.