Ford and others use a more deeply finned diff cover to help with temps on high performance models. BMW M cars have them. I put one on a 1995 M3 and put on a temp sensor at the same time. Never got hot enough to worry about even during long track weekends. Ford makes a deep finned unit for about $150 used on the GT 500. I have one on my Cobra. Try that first. There is a story oft told of a Shelby incident with a Daytona coupe. Driver never switched on the electric pump to the diff cooler, it overheated, brought into the pits, oil "bubbled" out, caught fire in the pits and put out. I have seen some video of it as well. I even think that Shelby helped put it out. Some Daytonas had a diff oil cooler vent within the rear "dish" about 6 inches tall by 16 inches wide. Usually messed over. Usually placed where license plate was put on right side, lower quarter.