Hey pozz welding your own headers is a cool idea probally cheaper too .I would definately use a tig welder use ER70S-6 filler rod either 1/16 or .045 diameter . take your time tack everything up first before welding solid. I definately would not use a flux core mig ,use sheiding gas , unishield mix and .030 wire ,same mild steel no. Good luck ,write back