I found this at Peacemakers March 14. By serial number late 1972 early 1974 manufacture. Posters on Ruger forum advised early low backstrap grip contour.
My fathers issue revolver when working for a government three letter agency was a SS Ruger security six. He purchased it when they mandated semi auto for carry. I still have it.
Thanks Zebra, I didn't think to ask the maker (Texas Grips) since he only offered smooth grips when I bought them. He now offers checking and will do mine. Sent them back with payment to have Spanish checkering. I'll post new pics when they come back.