I assume you are talking about a Superbird. I bought NOS decals for my Superbird from Chrysler back in 1980 and finally got around to using them a few years ago. The Plymouth and nose black decals were stored inside all that time and rolled up in the original boxes, which may have been a mistake. The nose and wing Road Runner decals were in their original envelopes Be very careful with the Road Runner decals, I found they needed to be removed from the backing paper very carefully as there are several parts and the Road Runner and Superbird letters are easy to crack. The nose black decals were not a problem. The quarter panel Plymouth decals would not separate from the backing paper and I ended up taking them to a local sign shop who was able to digitally scan the decals and then cut new ones on a reflective adhesive that looks to me to be the same reflectivity and gloss as the originals. Mine are white. For the correct colors I would carefully use the Road Runner decals on the nose and wing, as for the nose black decals and the Plymouth quarter panel decals, worst case the aftermarket are probably close enough that nobody can tell the difference.

Good Luck.