Posi needed!! Please help

If you run a short tire( and I'm guessing in an early Dart that you do) and you drive the highway more often than not you might want to look for a 2.94 out of an Imperial. They are still low enough for good take off but tall enough that you don't have that engine drone at high speeds. I have a 1970 340 Swinger and with 3.23 and the original 14 inch tire(about 28 inches tall) it would seem like I was always pushing it at highway speeds, not the rpm range that the engine desired. With 2.94 it would cruise 65-70 all day without the noise and extra fuel consumption. If you fancy yourself a stoplight racer then stick with the 3.23.