This is great information. Thanks! If or when I get one to rebuild, I'll be sure to try removing the input bearing first to verify it's feasible. However, I agree drifting a replacement bearing into place seems challenging and a risk to other internal parts. Plus, if the new bearing or its installation affects internal tolerances, how can you check and compensate for any needed adjustments? If drifting the bearing isn't feasible or wise and you want everything spot on, a teardown seems the best route. Hopefully, I'll be able to find out first hand sometime soon.
Lastly, my other tranny lament has been with the pilot bearing in the flywheel. I've had two seize, each time wearing a wide groove near the front tip of the input shaft; can't be good for the input bearing. Use a plastic/rubber sealed bearing. The metal shielded bearing the tranny shop installed seized after less than 30k miles.