The speedo adapter will work from any 3 spd, 4 spd or auto except the larger fitting used on the TH400 and later trans. G.M only made one small fitting. Not a bad idea to change the o-ring seal on it when you install it. As for the gears, they come with teeth ranging from a low of 15 up to a high of 22 (to count the exisiting teeth on your gear, turn it sideways with the long stem facing the ground and then count around in a circle). From past experience I have found out that a 1 tooth change will change the speedo by about 5 MPH. These gears are still available from the dealer (eg. part # 3987917 is 17 teeth: part # 3987919 is 19 teeth) Hope this helps.
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Ontario Inliners
1940 Chev Sedan
1954 Chev Custom
1965 Chev Pick-up
