Well, I used to have a picture of the difference in the upper and lower pieces, but it's on my old camera hardware. The difference is slight, but there is a difference. The long side of the trim is longer for the upper than the lower to match the slight difference in profile when matching up to the taillight. You can use the upper on the lower area without modification, but there is a slight mis-alignment where the profile meets the taillight.
FYI, the piece that Metro makes is actually the bottom piece. When this piece first came out I asked Joel at Metro which piece he patterned the repop after, as the lower piece is usually the damaged one. He said he didn't know there was a difference when he tooled them, but just happened to get lucky and tooled his repops on the lower piece. Lucky for him, as the lower is always the damaged piece. If I can find that old pic of the difference in profile, I'll include it here. I only have a lower on the shelf and ain't gonna take my upper off!!! Geof
