So I purchased a used 95 mustang GT convertible I got some factory copper sp-450 plugs to put in it when I pulled the existing plugs they were from bolt shoulder to the tip a half inch longer then the ones I bought turns out the plugs in it were sp-493 platinums but on research I find this to only be used in cobras not the gt so I started trying to Id the engine best I can tell it is not a cobra engine and I can not Id the 3 bars of a GT40 head which I think also uses these plugs so what's the story are they just the wrong plugs? they been it for a while so I guess they weren't hitting anything it was throwing random lean codes and breaking up around 5500 rpm so I decided to put in the plugs I bought figured there shorter shouldn't really hurt anything after a hard test drive it seems stronger pulls clean all the way to redline and no check engine light yet I'm just still kind of nervous if I have the right plugs in this thing it has the factory crimped headers on it and I can access plugs fairly easy on it if that helps at all