I have made 1.5" headers by using packed sand and renting a tube bender. It takes a bit of patience but you can make a very nice bend. The trick is to use totally dry sand (dry it in the oven if you have to) and pack it as tight as possible. Cap one end by welding it if you can, then fill and tap the pipe to settle the sand. I was told to tap with a solid object for one hour per inch of diameter, not sure if I did it for this long though!!. Then ram a piece of wood ( I used a potato!!) in the other end. Material was stainless, can't remember what the thickness was.