Hello,
I don't know if you are interested in reproduction route, but Classic Industries has the inner trim for the tail lights. You have to pain the center Argent Silver for non "S" car and as you already know, black for "S" cars. That's the route I'm probably going:
1969 All Makes All Models Parts | MA4736 | 1969 Plymouth Barracuda Tail Lamp Housing Inner Trim | Classic Industries
Or PG Classics has complete kit with the inner trim included, other sites you have to pick pieces to put a complete set together. The only thing I know that is not included is the red plastic caps that protect the mounting studs. Layson's and Year One carries them. Year One is on back order though, I'm waiting on 1 of the 2 packages I ordered:
306-BLKIT Mopar 1969 Plymouth Barracuda Taillight Kit
I hope that helps, I'm putting my "S" rear end parts together now.
Dan
