I bought my sq. butt new from George Cake Co, somewhere in CA, in 1960/61. Used stock grips with Tyler T, worked great. One of life's mistakes, traded it on another gun. Occasionaly fired a cylinder of +P with no adverse effects.
I've got a bunch of J Frames and only two of them with the Square Butt. While they make a hide out gun slightly less convenient for pocket carry, they shine when shooting with heavy +P loads. They handle recoil much better IMHO than their better looking RB brothers.