I made it - from some old KS tubing - The shape was done such that it has max flow -using straight pieces -IF I had some curves -it would have humped up a bit then curved back down to level The flow out of the exhaust port is away from the chamber so this is important for best flows . Look into the new ZDZ/ 3W engine exhaust ports you will see what I mean.
also why new headers have larger diameters than it would seem necessary - the path shape out the engine can change the power .