(Sorry about the huge picture)
Thanks to Brian Larkin over at The Tri-State Thunderbird And Cougar Club
who provided the best description of what our mystery plate is.
See: TSTaCC Forums - Ford Plate Decoder Help.
"this picture is of my fathers "93 cobra" h-pipe he bought at a flea market a few years back, the style of the cat tags match the one you have minus the year differnce. Your's is e7, for 87, the ones I have are e8, for 88. Take note the top 5 dgit numebr is the same, most likly that tag came off the pre cat near the manifold."