I need two new rear shelf speakers for my 280SE 3.5 coupe (1970). They are 4" X 8", with a 2 1/2" deep cone. The four mounting holes on the corners are spaced on a 3" X 7" grid. The old speakers cannot be reconed by Simply Speakers (parts no longer available). I tried J.C. Whitney for new ones - no luck in that size. Where can I find replacements that will fit w/o modifying my rear shelf?