NASCAR always required stock exhaust manifolds up until the 63 Chevy mystery engine. Smokey had a set in his garage that had a cast flange with tubing brazed on dumping into a 4 inch pipe that probably exited about just before the rear wheels. The Mopar cars started a similar setup late in the 63 season, and continued it with the hemi cars. The first Ford I remember with actual headers was not until 1966 late in the season when they were ending the NASCAR boycott. Bud Moore for sure had tube headers but they may have been constructed with a cast flange at first. The rules seemed to have finally evolved to tubing headers with a flat steel flange in 1967. At best as I remember.