Early 833 reverse

My newly installed (old)833 doesn't want to go into reverse. I did have the side case off for inspection before I put it in the car . I forgot to try the reverse . It seems like it is stuck somewhere in between. I watched the old mopar video and it states that while in neutral.Move the side case up or down a little will affect the clearance between the 1-2 /reverse safety . Going to try it hopefully tomorrow . Has anyone done this?