Deezel, Pull each spark plug. If one is exceptionally clean (i.e., it has been literally steam cleaned by the engine coolant), then that is the location where the head gasket surrounding the water jacket let loose. Unfortunately I learned this lesson the hard way sometime well-back in the past. Hope this is of some help to you.
85 500 SEL, 241,500 mi
90 5.0 Mustang LX conv.