The Ruger Speed and Security-Sixes came with for the most part with skinny service grips, made to the thrown away (my opinion). Back in the day we used to joke that when Ruger made his first gun, he purchased one tree to use for grips. And he was still using it.
There were only two quick fixes back then. You either put a T-grip on it, or you bought a set of Hogue's or Pachmayr's. I'm sure there were other aftermarket grips, but not many shops stocked them, and even fewer stocked them for a Ruger. I don't think I ever saw but a couple sets of Ruger factory target grips, and I know I never owned any.
I'll bet a lot of those service grips got tossed in the trash before the gun left the shop. I know mine did, and a set of Pachmayr "Gripper's" went on.