Bill, chrome trim in these areas (wheel wells, gutters, headlamp bezels and tail lights) is "Style Trim Group".
Taken directly from
www.camaros.org
The codes are divided into two groups, those with the Z21 style trim option, and those without the Z21 style trim option. (Since the Z21 Style Trim group also was generally included in the Rally Sport option, Z22, all Z22 cars are included in the Z21 X-code group. The only differences were the headlamp and taillamp lenses.)
with Z21 (or Z22)
---------------------
X11* non-BB, non-Z28,
including SS-350
X22 BBC
X33 Z28
without Z21 (or Z22)
-------------------------------
X44* non-BB, non-Z28, non-SS350
X55 SS350
X66 BBC
X77 Z28