sm465 top cover is stuck on truck will not come off

[Preacher141]

Here is my issue. I knew it had to be half way in reverse to put the top cover on and thought I had it. But, it will not shift into reverse. It is out of a 1967 C10. It will not go into reverse no matter what and now the cover only comes up half inch. Any ideas why I can not get the cover off and how to get it to come off? I searched the net and on here and all I can see is how to install it basically. No info on anything else.