You need to get everything in neutral so you know where it is. You may need to remove the driveshaft so you can tell when it's in neutral. You will be able to spin the output shaft when all is right.

Ferndale recently had a very similar problem. maybe give that thread a read.
https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=624914&page=5


1953 Chevrolet 3600
Fried Green T'mater (Vern)
In the Stovebolt Gallery
Caution: Political Statement
Man who runs in front of car gets tired, man who runs behind car gets exhausted.