Please school me on exhaust manifolds

I don't know the trouble with your existing manifolds.. maybe get a second opinion. 340 ($$) stock cast exhausts have been considered the best production manifolds for performance for years. A couple of years ago Mopar Muscle Magazine did a comparison and the 360 manifolds were nearly as free flowing as the 340's. Suprisingly.. IIRC, stock 318 castings were only a few ponies shy of the 340 & 360 lumps. Some small block truck exhausts are also viable choices. Of course after market tubular headers are made by several companies with a wide range of quality and price. Ebay, Craig'slist and swap meets are good to search too.