The Chevelle header generally fits a big car as well which isn't as important in a 1969 that left the factory with a BBC as it would be if you had a big block in a later year car or if you had an LS-x motor. The bigger the primary tube (2" isn't all that big for a BBC) the closer the fitment will have to be.
Getting back to answering your question; Headman builds headers to fit your application as does Hooker (caution competition headers have thinner walls which rust faster, and they do not come with a collector flange to bolt up header pipes. They also frequently have pipes that slip fit together for rapid access to motor parts between rounds; so read all of the footnotes at the bottom of the page). I would also check out Doug's website for a set.