I think you and I have the same problem. I've got a 2000 70hp johnson that I'm trying to drop the lower unit and the shift rod release is hanging me up.
If you have the seloc manual for these engines it says that there may be a pin that you can see from the starter side of the engine. There may be a hex head screw instead. It seems like there is variations in the attatchment set-up. You are supposed to push to pin to release the shift rod. Let me know if you have any luck.
straight from the OMC shop manual. remove the shift rod screw. photo shows it as the hex bolt located under the lower carb and a few inches aft. i looked on my 50 b/c i already had the starter removed and you can clearly see it down low where the rod goes south. I always stuff rags around the lower cowling area in the area I work to keep those small fasteners from getting lost in that southern black hole. you won't retrieve ss fasteners with a magnet but I love my extra long needle nose pliers for these jobs. let me know if you need more info from the manual
