Now you might be saying... Wait a minute, can't you get the gear dogs undercut?
Normally yes, however, the splines that the gears attach to the shafts on are worn out.
And the snap rings that hold the gears in their relative positions are completely wallered out....
Definitely something bad happened here..
Then we discovered the problem...
Here is another case out of my top secret stash..
See the steel insert where the output trans shaft goes?
This engine had no insert..
That means that the output shaft was just flopping around in there...
It's a wonder the engine did not grenade..