I got a 95 mustang and the owners manual calls for a motocraft asf42c spark plug which the thread link is only about 3/8th of an inch long and i havent changed them since i bought the car but they wond go in the head the ones i pulled out are a bosch platinum hr8dpx spark plug wich the thread links are about 3/4 of an inch long and the holes are angled back in the heads can anybody tell me if they are aftermarket heads or why the original plugs wont go in.