It could be an adjustment at the lever or it could be a broken lockplate or shift collar in the column. The adjustment is easy. Loosen the nut on the lever at the trans. Put the trans in neutral. Put the column in neutral (might be hard without an indicator). Tighten nut.
If the lockplate or shift collar in the column is broke you'll need a new one. Wild horses has them. Well I know they have the collar, not positive on the lockplate. I've seen them for sale somewhere though. You'll need to pull the wheel, turn switch and collar off to fix it. WH has a video on youtube showing how to replace the collar. Here it is:
http://classicbroncos.com/forums/showth ... ch+article