for some fun reading here is a thread I posted some info About Speedo part numbers and such.back in 2006
https://forum.ih8mud.com/threads/speedo-gear.118664/
The drive gear should stay in place once you slide the ebrake drum on and torque it up. What’s the tooth count on that speedo gear? Looks small in diameter doesn’t look like any parts are missing other than the drum to hold it all in place.