The .38S&W seater die would work fine, there's only something like ten thousandths difference between that and .38sp. Close enough that, depending on tolerances, sometimes you can use .38 S&W brass in one. I used .38S&W in my 1892, until I got some actual LC brass. Woudn't fit in most of my other .38SP guns, though. As for substituting other caliber dies, I think one of the dies that came in my .38S&W set(lee) is marked ".38 auto" I guess Lee thought they were close enough!