Just lever that bit with a screwdriver, that drum has about 1/4" of back and forth play. Hell, I bet if you put pressure on it with your finger it would move out of the neutral switch's path.
This is the drum and what it looks like inside there
See the brown strip on the outside 1/8" of that shiny surface towards the end of the drum that's right at the tip of the pliers? (The very surface your stopper is hitting.) That's from oil over time with the drum having that 1/8" of surface exposed under the shift cover. That 1/8" is play in the drum. I emery cleaned that 1/8" strip of oil residue off that surface, and the drum moves back and forth that much. Once you push it out of the way and install the neutral stop, the stop it's self will hold the drum in a static position. It has that play because the stop is removed. Just push that drum towards the shift side and it'll move out of the way.
Here is a shot of the drum (lower left) before removal that shows it sticking out that 1/8" and you can see the oil strip I later cleaned. Yours has just slipped back into the engine since the stop was pulled. push it back out and put your stop in.