My 37 Buick came from factory with a 4.44 rear end gear so I pulled the torque tube and used a 2.73 from a 1970 El Camino (Chevelle). This was fine for the old straight eight in this part of Texas with no hills but it ran out of poop in Missouri. Decided overdrive was the way to go but not smart enough to figure out on paper what gearing was needed to put me in the peak of the torque range at 65mph so tried several gear combos which threw the speedo off with each change. Finally wised up and stuck my Garmin gps to the windshield to get dead accurate reading no matter what gears or tire size. Now I have a gps speedo which I'm making a factory looking rectangular mount plate to accept both the stock gauges and the gps. Am a happy camper that will never fight cables, gears, or ratios again on any future project.