The infamous and rare VOE exhaust option was only offered a few months on 1970 GTO's before it was pulled by Pontiac because of tightening smog regulations. This recreation of the VOE exhaust was originally hand engineered by a guy on PY forum and then his design was carried forward by a large exhaust manufacture. If you want to read this very cool thread on his development of it see the link below.
After 37 Years, the Humbler VOE GTO Returns - PY Online Forums
Brian