Hi Leanna the 67 trunk trims are the ones you can swap for use for top and bottom, they need a bit of tweaking to do this but can be done. the 67 also uses a center trim. 67 has 3 pieces on trunklid, 68 uses 2 pieces that your correct do not interchange top and bottom, though i have not seen those reproduced yet. And 69 which uses a 1 piece trunk trim panel.
I have owned all 3 years starting with a 68 fastback in 1988, and my current 2 cars 67 coupe and 69 coupe.
