hi mate first look at my thread "zetaboostboy area six jwrc fiesta update" the silver top is what i would use for the ease of the engine mounts etc, as for the gearbox i thought all the zetecs had the same bolt pattern so you can use most of the ford fwd gearboxes.i believe that the silver top has beefier bearing caps and are stronger, but the black top has a better flowing head.its all about how much power you want really.my silver top head did 522bhp so its plenty for most people. you can put a black top head on a silver top engine with some work but it would be best to go for a st170 on a silver block as the st170 is by far the best cylinder head, ask ian howell at area six motorsport to do the head if you want big horsepower hope this helps