Early A-body SBlock headers
There's lots on this topic over here ->
http://www.enbcom.com/discus/messages/394/418.html?1126794002
There's a guy on the net with a '66 Barracuda that is running the HP 340 stock manifolds. If you look at another site, someone did dyno tests on these stock manifolds vs. headers and there's not a lot of difference.
To make the HP manifolds fit (we're talking about the '68-'71 manifolds also known by their part numbers ending in 553 and 549) he had to change his steering column coupler to an aftermarket u-joint style.
This is what I'm planning for my '65 Barracuda. I already have the manifolds, just need the coupler and the guts and I'm all set!