That's the seam where the sheetmetal top is welded to the A-pillar sheetmetal. Usually it's leaded from the factory. You'll need to take the paint down to bare metal and see what's there. Could be a PO reskinned the top from a previous sunroof. Take it down to metal and put up new brighter pics.
alright, i'll do that some time when i get a real digital cam.
but, i really do doubt it was a sun room because i'm only the 3rd owner. and the 2nd owners bought it for parts (2 friends with mustangs), but they decided that it was in waaaay to good condition to be a parts car so they gave me a real good deal on it because i said i was going to restore it.
but chances are all i have to do its make a patch (metal) and weld it in place?