allit probably needs is a new shift cable(intermediate cable). 2.5 hours labor plus $85 parts. But it could easily open up a can of worms, you know, "while you're at it you might as well fix this... It can snow ball quickly, next thing you know you're handed a $2000 repair bill, If you're really interested, have it checked out by a mercruiser technician.
Thers a guy in town with a 76 I/O who had teh same problem. Took a hammer to the linkage. He has reverse now, but no drive now. :-/
Guess he whacked the wrong piece. ;D