Ditto on the groove, I have one too and I think it was done at the factory to grind off some casting. But, I'll keep an eye on it. Pushing the bolt back enough to catch the Safety, part #13, can be a bugger. I also had be bend the Safety so it would hold the bolt back enough to expose the Slide Retainer Pin, part #9. To push it back far enough I had to push from the front of the slide to get it back, after it was unloaded of course. When I finally got the Safety to work right and the Bolt to go back far enough, I locked the bolt open and left it that way for 2 weeks. It seems to make pushing the bolt back a little easier after that.
The Sear Assembly, part # 12, only fits one way, with the slope facing forward and the flat side back. So, after compressing the spring for a couple of weeks, it's easier to rack the slide back to load a round, but getting it back far enough for the safety to hold it open is still a chore. Please, let us know how you make out.