Road Runner Nest

Does anybody here know who owns the rights to the Superbird logo on the wing? I know that WB owns the Road Runner but Plymouth modified the Runner for the Bird.
I am working on a show car that will have a Chrysler powerplant and I want to use
the Superbird logo without the words.
I read something years ago that once something was over 30 years old it was public domain. Is this true with the logo?
Thanks,

It's now Time-Warner that owns the rights to the Road Runner cartoon and they're guarding it tightly for their Road Runner internet service. That's why you don't see anything else using the Road Runner.

Public domain? I don't think so!

Why not just buy the superbird decal and omit the lettering? They're all separate letters anyway.