Randy is spot on. If you want to see how far out Ruger SA grip frames can be from being flat, visit someone’s shop like Alan Harton or Dustin Linebaugh. Last time I was at Fystinscwe went through the “decking” of machine flattening of a carbon steel bisley grip frame to get it ready for fitting a set of bighorn sheep grips. By the time you locate the low spot (which Dustin said is almost always in the same area) and machine the rest of that side if the gripframe to match you have more than a few minutes involved. Remove part from fixture, flip it over and go through the whole process on the other side and only then to have a flat and consistent surface to mount your grips to.