I'm in favor of the steel, particularly while you're in the "cut and try" stage. Once you've got a good prototype in progress, you might think about duplicating it in aluminum, maybe with a piece of large-diameter conduit for the main runner, and smaller pipe for the connectors to the head. It would be lighter, and look better than welded steel, once the design is finalized. I think I'd use exhaust tubing of different diameters for the prototype.
Jerry

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