Front sight: I used needle-nose pliers to remove the nut on the underside of the sight. Added a dab threadlocker, held the sight straight, and tightened. I think it gets cockeyed when the sight rotates as the nut gets snug. This task is much easier if you disassemble the gun and remove the barrel (I’ve done it both ways - working with the barrel itself is much easier),
Several here have used the stock, plastic rail without issue. There is also an aluminum one available on BerettaUSA.com.
Just be careful when tightening those screws that attach it to the receiver - they are fragile, and it’s too easy to break the head off the shaft. Ask me how I know...