Re the fuel pump push rod the "retainer" is the baffle tube. It pulls out. If you gently tap it side to side it will loosen and you can pull it out. I show one in a recent video. The fuel pump should have a corresponding tubular extension that is a snug fit down the center of the baffle tube. While an engine will still run ok with either piece missing, the breathing system and route the air takes when flowing through the engine is compromised.
This is the video you can see the baffle tube at about the 25:30 minute mark.
https://youtu.be/or1k-tQGEIo
Mart.