I doubt very much if your Official Police of that vintage has a rounded butt. Rounded butts first came in on 2" O.P.s, for less "printing" of the outer garment in CC.
NYPD also had a special run of 4" O.P.s made up with the rounded butt. Colt's "shortlived" Marshall Model circa 1954, was just an O.P. with the rounded butt and different roll marks, available in 2 or 4 inch, blue or nickle.

Grips and rounded grip frame are very distinctive, like the round/square butt choice on S&W M&Ps.

Thanks for the inquiry

Bud