Correct shoes. Made sue the short shoe is in the front on both sides. Brake cylinder is compressed as far as it will go and I held both sides and gently tapped the shoes until they sat perfectly in the middle. I’m at a loss.

I had to look this up, I guess it won’t let you push it into reverse if it’s got any sort of forward momentum whatsoever. I used to think about this a lot when I was learning and putting it into 4th.