904 Transmission Stopped Going Into Gear

Yes, that much end play in the rear shaft is normal when the tailshaft housing is removed. I think the rear bearing is not seating all the way into the tailshaft housing. Or the bearing is not seated onto the output shaft. I paused the video but it got too blurry to tell. Look inside the tailshaft housing to see if there is a foreign particle embedded. The only reasons to remove the tailshaft housing is to check and clean the governor and replace the governor rings. If a governor is not stuck and the trans is starting off in first gear and shifting at all, I don't recommend the beginner to remove the tailshaft housing; not even the planetaries or even the little snap ring at the front of the output shaft. Just check the rear band by loosening the adjuster then reset it and leave it alone. Air check the servo. You could install the tailshaft into the housing then install them both together. Tap wherever you can to make sure the bearing is seated first.