I think you will have to figure out what it takes to move the gear out of the way. There are illustrated parts lists at
Kubota USA that show how they go together. Unfortunately it looks like bearings and clips at both ends hold the shaft in place (assuming that I looked at the correct diagram). So that means more disassembly of the tractor I believe. It may require a split of the tractor to gain access to both ends of the shaft.
Otherwise, you could think of ways to modify that from a one piece “lever shaft” to two shorter pieces that can be installed and then joined back together. I originally was thinking to cut the welded bar off, install it and weld it back together but not sure that is a viable option. I guess a good welder using a gas shield process (MIG or TIG) could do that without making too much of a mess. I would not use SMAW (stick) due to messiness unless you can protect the gears and case from spatter.
I would think a good machine shop could come up with something that could be bolted together after it was installed but it might cost too much! I can think of a joint that is keyed together like a coupling or sleeve or another where the external half becomes a bolt that screws into the internal half. Then some roll pin through both parts to keep it from unscrewing.
More damaging to the case would be to machine out the hole large enough to get that part in and then add a cover to replace the existing hole.
Or possibly just put it in one range and put it together and only use that range for a while. If you know you are in low range most of the time that may be the easiest way. But since you even noticed that it wasn’t working I imagine you need both ranges to efficiently use the tractor. I only have five acres so high gear in low range can get across it fast enough, but I can see if there is longer range travel that high speed range is needed.
