None of my 1968 Shelbys (GT500KR, GT500KR, and GT-500) have the plastic piece. Neither does my 68 289 Metuchen coupe.
All of my 1968 San Jose dual exhaust cars (302 GT, 428 HCS, and 428 CJ FB) have he clips and plastic strip.
My 1968 single exhaust San Jose coupe does not have the plastic piece.
Scott