My father-in-law is an authorized dealer for goodmark and dynacorn... and they do not carry any reproduction tail panels. However, I just checked the dynacorn website and found this in their FAQ's. Question: Any word on the '69 firebird tail panels? Answer: "Nothing yet...keep checking the New Parts tab, when in they will show up there for sure." So hopefully they will have them soon, because my project has about 2 inches of filler on its backside.
