Is a model PS the same as a model P?
The PS addad a magazine safety to earn extra ATF points for importation after the 1968 GCA. OTW same as the P, as far as I remember. The A was the 9mm and the B was the 38 Super/9mm Largo. The PS is a larger frame to acommodate the 45ACP single stack 7 round mag.
The safety is under one of the plastic grips (left IIRC) and can be lifted out without any tools allowing normal operation, including saving your life with that last round in the chamber when the magazine is not in the well.
Still have on with some of the chrome plating on it. My first 45 ACP