I don't know the build sheet codes.
But, you could go to this website and look at the 81 Trans Am gallery, where you'll see many pictures of 81's with the different colors and decal combinations. So, one of them will likely be your combination:
http://tran-zam.com/
Personally, I like the 79-80 decals better, which you could use instead, if originality isn't too important to you.