Well, a 318 never came stock in a 67 Barracuda, so you should probably be looking at listings for a 1968 Barracuda 318. The general consensus is that the only headers that are a clean fit are TTI. Doug's, Hooker, etc. all require bashing or bending, or so I have heard.
Be aware that running a second tailpipe over the axle in a 67 is difficult because of how the fuel tank strap is secured on the right side. It can be done, but it will be tight, and you can't run a big pipe. 2-inch or less is recommended.