I stripped out one of the spark plug holes in my 350. I can see no threads left. How do fix this. I know you can rethread it.What I'm asking is how big a PITA is it with the head still on the motor? Can I get the kit at NAPA, and if so does anyone know the part number? Also how well do they work. It is a bit of a thumper, the engine that is. Any help will be appreciated. Thanks.