dont you think a better way to quiet the noise would either have a cover that sticks our further (i wish). or a couple gaskets on the cover to make it stick out further.
You could do the outside of the cases for sure but it would be a astetics thing there. The stuff I use is Waker T-442 Part number 1830858C1 in the 4.7 ounce squeeze tube ($17)or the caulk gun sized tube which I use part number 1830856C1 ($27) I think the smaller tube should easily do just ther clutch cover.
Its made for international trucks but im sure ford uses thier own equivalent so either dealer should have it. Its the best gasket maker. Agressive adhesion and high flexabilty are its best properties.