I did just as St. George described with tape,or you could always fit the grips first and then have the back strap and trigger guard off to have them plated,assuring a perfect fit. Believe me if I can fit them perfectly any one can, although I had the same fears as you before doing the first pair I got from Larry. When talking to him ,he went through the fitting process with me. He is a artist, you won't have any problem doing it yourself. Call him up and talk to him, a nicer gentleman you will not find ,he will offer to sent you some practice panels ,fit them first. It really wasn't that hard to have come out perfect. Just a suggestion for your 51 navy, I would go with the one pice grips instead of two pice ,with a screw,JMO Edit That is sad news ,I know when he did the first pairs for me ,he said he had to make the butt portion mold using that section from a ruger super blackhawk Adios Sgt.Jake