Crank end play, destroyed converter, 408 nightmare

I have a friend that I believe didn't properly seat converter. I'm going to insist we jack up and crawl under. Unbolt converter. And reseat. I'm assuming 727 is like any trans? If seated should spin gears. If not? You would know by sound and inconsistent spin?

Speaking of convertors, I saw part of an automotive show on TV , where they drove the convertor in the trans. with a big mallet , before installing it !