I´m not that sure on Chevelle-facts but wouldn´t certain emblemholes or lack of these in the original fenders, combined with the original SS-hood tell us something ? Or did all 1969 Chevelles have identical fenders (with certain holes) regardless of what engine it was equipped with at the factory ?
Also, the original tailpanel on an SS-car has the SS-trim attached in elongated holes, so a COPO with SS trim would have drilled round holes in the tailpanel. Even if the elongated holes have been welded, I think it would be possible to make something out of it.
