If reverse doesn't move at all, I'd wonder if the other gears are fully in neutral.
Sometimes a worn shift lever will allow you to move the lever around as if you are in neutral even though one of the gear selectors are slightly out of the Neutral position.
The selectors are set up using a system of detents and a shuttle that makes it so that you can not move another gear selector at all unless the previous one is perfectly in neutral.
I'll try to post a photo of what I'm talking about...hold on.
--Mark
1973 SIII 109 RHD 2.5NA Diesel
0-54mph in just under 11.5 minutes
(9.7 minutes now that she's a 3-door).