I got a buddy to 3d print a few pieces as an experiment to see how well it would work. It was surprisingly effective, and at $0.30 per piece for filament I might consider making a full set when I am ready for exhaust work.
Though I did see that Holley had started making equal length cast iron manifolds/shorty headers for a few engines. That concept appeals to me as well.
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
We use defroster duct with holes punched in it so spray foam can be squirted inside. Once foam sets the tubes are plenty rigid to use as patterns for a tube bender. Pic of header for a Studebaker Golden Hawk---not something one can buy off the shelf.
One of the neatest exhaust systems I ever saw, the owner cut the pieces to fit, super-glued them together to verify fit, and then welded it all up when he knew it all worked together. You had to see the finished product to believe it.