340 exhaust manifold?

There is an Early Abody sub forum.

http://www.forabodiesonly.com/mopar/showthread.php?t=103592

I have a 1964 barracuda 360 stock with high rise and 4brl carb and a 4sp.,
I was looking to put on a set of fender well hookers or 340 manifolds, would I notice much in the way of power? If I go with the 340 manifold what year would I use and are there any fitment issues? Thanks