"A beater" ? IMHO a steel frame is heavy duty, a stainless steel handgun is all-weather, neither rain nor snow nor sweat will bother it. Target shooters never clamored for lightweight frames.
Can't get that 439 slide to fit ? Interchangeable parts-won't. I bought a small letter slide for my Colt Mark IV-I had to use some grinding compound to get it to fit.