need help Bad-excuse me for being stupid

changing plugs in the Duster.the plugs in it now are Champion RV12C. They have been in there 10 years. look ok to me. thought I would get new ones in it. went and bought a new set. decided to keep the same ones in it. did more research on these. It calls for RJ14YC plugs. There is a difference in the reach.RV12C has a .460 and the RJ14YC is a .380 reach. I went on Summit's site and according to the application for the RV12C plugs, they are for a Chevrolet. Now I didn't put these plugs in the car. I was in a rehab hospital when this was done recovering from a brain aneurism/stroke. I just assumed when it was done they put the right plugs in it. This changes things. How much will the difference in reach mean here and also if these plugs have an application for a Chevy, why the hell have they been working so good in the Duster. will I have more power and run better if I go to the RJ14YC that has the difference reach or a different brand plug.