Hi; I can share these bits of information with you. I have an original 70 ls-6 built in Atlanta(04d)that I bought in 77 with 23,000 miles on it . It has steel. I have an original paint 40,000 mile 70 ss conv that was built in Balt(04a) that has plastic. I have an original paint 70 coupe built in Flint (053) that has plastic.Of the last 2 70 454 coupes I restored 1 with with 23,000 miles had steel built in Kansas(04a) had steel, as did the one built in Balt (02c). It has nothing to do with LS-6 , Air conditioning or so on . Chevrolet used platic liners in 69 at some point they had a problem with Snow and Ice cracking them and redesigned the bosses around the bolt holes for more support. The plastic inner fenders that you see today were mostly destined for Monte Carlos and have an extra hole just above the 2 that attach it to the firewall. This bolted to the fender support that these cars have. It would seem that most of your Atlanta built cars have steel, At least the many I have seen over the past 20 years. To answer your question Steel is your best bet as they look correct and fit pretty good. The plastics that are available to the genral public for a reasonable price just don't fit the bill. Thanks and good luck. [img]/ubbthreads/images/graemlins/
[/img] Jim