I believe this car listed below was equipped with headers.
I do not know of any 60s/70s cars tested when new that ran less then 13s without headers. There is a Car & Driver test of a narrow tire 1966 427 Corvette that was listed in the 12s but this test is not valid. Car & Driver admitted that they exagerated some test numbers or just made them up.
5 1969 Roadrunner
[email protected] 440 Six Pack 390 four-speed 4.10 SS 6/69