OK, so the "gill" area is original sheet metal? Or has this been replaced or at some point (original, NOS or repop) or straightened after a collision? You can get the outer skin straight after a collision, but the indentations are a different story. That piece can look straight by eye and gauge, but the inner portions (each of the 6) are a PITA to reform after a minor dent.

I don't know..If you replace the uppers (ones that fit) with the lowers, what is the result? As well, measure the depth and length of the upper gills..I say take some "Pam", spray on the gill areas in question and take some modeling clay impressions of the uppers and lowers and measure the difference.