it is a munci 1968 M20. the drive gear is metal, the driven gear is plastic and has 22 teeth looks grey to me. can i measure the driven gear OD and help determine the OD of the drive circle gear. i count 6 teeth on the drive ,it could be 7 its hard to count them through the small bullet hole. i have 3.31 gears and 28" tires i have searched this subject several times and get confused.