Tom,What does your reference show for the number of teeth on the drive gear? 7 or 8 possibly? I found a great site with a lot of information on speedometer gears and related items. They have a ratio calculator, tire size calculator and a ton of gears. They offer 16 through 23 tooth gears for 57 Fords, the same part # for FOM or Stick. With a 4.10 ratio and 7 tooth drive gear, a 21 tooth driven gear would work with most tires in the 26.5 to 27" range. With an 8 tooth drive gear, the 23 tooth would be as close as you could get. I may have to pull the speedo gear, mark the drive gear, rotate the shaft, and count the teeth. The site is transmissioncenter.org I called them and the person I talked to was knowledgeable and very glad to help.