The 340 headpipes are different between the 1970 and 1971 e body applications. See the following link.
http://www.accurateltd.com/70-74-E-Body-Small-Block-318340360-Complete-Exhaust-Systems-_p_239.htmlOrder the headpipes that correspond with the exhaust manifolds being used. The 1970 340 exhaust manifolds , (49,53 castings)
had welded hp flanges on the headpipes and used gaskets. The 1971 headpipes used a floating flange and ball joint connection arrangement that did not use a gasket between the manifolds (623,621 castings) and the headpipes. Hope this answers your question.
