You are correct, probably from 70'. The head port will leak at the lower side of the manifold. I forget the correction for this, but it is a gasket change. Dry fit it before installing. Don't use the 318 manifolds or you will kill the motor on performance. Not sure what you are building but if you don't want to spend the big bucks on the correct manifolds, then why not go with a good set of headers for about the same price and gain a little HP while at it.