If Pachmayrs are recoil-uncomfortable, that's a tough one. I find later rubber grips like Uncle Mike's ergonomically superior, but I don't know whether those were even made for square butts. Alternately, you could try putting a grip adapter on the gun; some people prefer the somewhat rolling motion of the smoother original wood grips to the friction of the textured rubber which transmits more of the recoil sensation to the hand surface.

I have a period-correct Mershon adapter on the 1959 square-butt Model 36 in my collection and find it quite pleasant to shoot.