I suppose you could use HREW tubing but you'll have to grind out the raised weld inside to be able to insert the threaded bungs. As for the shackles, that's the only way I've seen them done. You may want to visit your local steel shops because they will probably not go into detail about their remnants. They typically just have them in a pile or on racks and don't keep track of what's there. You gotta pick thru it yourself, but it can really be worth it. Where I get steel, rems are sold by the pound and are about a third the price of virgin metal. Even if you don't find what you need you'll always find cool pieces for other projects. It's like an Easter egg hunt.