Hi, and welcome. If you have a 2 1/2" 66, it came with walnut round butt Magnas without the diamond around the screw hole. I believe the current new service stocks are a laminate; they will fit but are not correct for the gun, if you are concerned about that. This is a link to a completed auction with the 2 1/2 " gun's original stocks:
Smith & Wesson- Mod 66-1 2 1/2 inch : Revolvers at GunBroker.com
If a 4 or 6", walnut target stocks with the "football" cutout.
Smith & Wesson S&W Model 66-1 357 mag NR! : Revolvers at GunBroker.com
Now that you have this information, you must post photos after you find the correct stocks
