A foot to go suggests it's binding in the transition from the crank sprocket to the tensioner guide. Thankfully gsxr has this picture from a 603 which should be identical to a 602 for this situation -



If I had to guess, though, I'd say it's binding between the IP sprocket and lower guide or lower guide and crank sprocket. If you're really stuck, pull the vacuum pump and basket. It might give you a clue as to what's going on or at least a new leverage point to tease through/back the chain.

Might also be binding by oil pump chain where chain width clearance is tightest.

Sixto
87 300D