Wow, that was a great video! It looks like the burrs created by forcing the transmission into gear were interfering with proper operation. Were the synchro cones completely worn out on this tranny? Or is it possible to force it into gear (before synchronization) even with a working synchro? I understood that it would be more or less "locked out" until it all came up to speed (assuming the synchro is working properly).
Another note is that the 2nd gear dog teeth are not symmetrical like the 1st gear teeth. I don't have a photo of each gear seperately, but here's a photo of my blown up gearset. I believe you can see the symmetrical dog teeth on 4th (like 1st in your video), and non symmetrical teeth on 2nd and 3rd. Any insight on why they are different?