i have never heard that one before. all the gas blocks i have seen are attached by allen head bolts. most often two on the bottom but some have two on the sides.
i can't believe S&W would use a non standard gas block set up.
the sight-base/gas blocks are attached by tapered pins pressed in the sight base. i haven't handled a s&w with a gas block only the ones with the front sight base.
i would guess the gas blocks are just bolted on with a lock-tight. but that is just a guess.