Yah, a bit beyond the average fabrication job, I have been building headers, not simple ones but real headers since the mid 70s. My first customer set was built on a rather radical '70 Camero road coarse car. I hand formed the steel fender flairs, not flat wrapped sheetmetal, they were all formed with hammer/ dolly, The headers were full long tube tuned system, muffled to meet road course sound levels for club events.
On these headers, primarily due to cost I chose to use mild steel tubes with stainless collectors. My justification is I have a set of mild steel headers here that I built in 1976 for my track day Colt. The headers are fully serviceable, just not in use since they require the floor to be raised up as needed for generously lowered cars, as in 4" lower with full suspension travel.
I thought I would have the last tube done by now but just did not get it right, It was tight to the frame rail, so I did a better job marking the other tubes as a guide and back on the bench. I chose to pour my whiskey and be done for the day.