I'm in the process of gathering parts to build a 1968 3925660 M20 for an upcoming project. I would like to replace the plastic speedo gear and retainer clip (as other members have done, talked about in other threads) with the steel 8 tooth gear as used in the 1967 010 trans. Would I be correct with the 8T steel gear, part #3708145 to replace the plastic gear? I also understand that 6261794 and 3924097 are replacement numbers for the same part, are these numbers correct also? I will be using the black 23T driven gear, 3860346, for 3.73.
Are the main shafts the same between 67, (intended for the steel gear), and the 68-69 main shaft intended for the plastic gear. Is this a direct conversion? My main concern is that the steel gear will end up in the right spot to mesh with the driven gear, being that it doesn't have the spring clip to hold the gear in the right spot.
Since the 1968 3925660 case uses the 3884685 side cover, Does the 1968 3925660 also use the 3851326 front bearing retainer, or the 3915020? Which front bearing retainer is correct for 1968?