Here's an update and a tip I found on YouTube. The new safety detent spring and plunger came Saturday and I put it in in less than a minute on the second try. I saw a Youtube video that included a suggestion to use the broad side of the recoil spring guide rod to hold the plunger down while pushing the safety over it. I thought that was no better than my flat precision screwdriver, so my first failed attempt was with the screwdriver. That didn't work so I tried the guide rod and it was easy. It's broad enough that you don't accidentally let it it slip off and, unlike a screwdriver, you are holding it from above rather the side. Just push the safety down and it pushes the guide rod off ahead of it. At no time is the plunger uncovered.
Oh yeah, I covered the drain in my shower, got in, closed the door, sat on the floor and worked on the gun. My wife was laughing, but that spring and plunger weren't going to get away this time!
Give it a try, it works great.
Chas.