This construction is open to several welding processes. Of course GTAW (TIG) requires the least finishing, which is why Carlyle favors it. But GMAW (MIG) and FCAW (flux-core) will indeed suffice, provided you don’t mind ropy beads or lots of grinding. But there’s an even more appealing option: The flanges withstanding (which work best with GTAW and almost as well with GMAW), this is an application practically made for oxyacetylene welding.
Acetylene welding is appealing because it produces weld beads barely harder than the base metal. That’s good because soft materials move readily. And whether by heat cycling or engine vibration the metal in headers moves quite a bit. The boundary between the soft pipes and relatively hard electric weld beads concentrate stresses that often cause the metal to crack adjacent to the weld. Gas can produce beautiful, small welds but it just takes more practice.
We’ll also expand upon another piece of advice in the captions but here it is in a nutshell: start with the side that has the rearmost-offset cylinder bank. One bank of a V-configured engine sits slightly behind the other. With a few exceptions (big Olds, Poncho, and the late OHV Caddy for examples), this means the passenger side, and on some engines, the offset is huge (roughly 3 inches for big Chevys).
Doing so establishes the forward-most position where the header ends. Start there and you can lengthen the other side’s header to match; however, if you start on the forward-offset side you may not be able to shorten the rearmost offset header to match.
Beyond that, though, the world is your canvas: primary pipe angle and length, cone angle and length, and construction style are open to your interpretation. As Carlyle worked he explained how fit and style largely prevail in lakes header design. Get a grasp of those and a mastery of some simple tools and you’re guaranteed a header that’s unique, just like your car.