Headers VS Manifolds

66cuda
For a daily driver/cruiser there is no reason you can't stick with the manifolds. I have a mild 318 in my 65 valiant and i'm planning on keeping the manifolds but upgrading to the 2.5" TTI pipes that bolt right up to the manifolds and go all the way back (the only mod you need to do is notch the tranny crossmember, as you already know). The complete H-pipe kit with mufflers is about $600 which is really reasonable actually (they're aluminized mandrel bent and comes with all hangers/brackets). You can't have custom exhaust made for much cheaper imho.

The next less costly option is to buy a set of spitfire headers (~$225, but only using manual steering box) and have custom pipes bent to the TTI's.

Good luck!