[Esprit83]

You may get by using a common type 308 stainless welding wire, but the "book" on stainless steel welding calls for the use of type 309 or 310 wire. The higher chromium-nickel content in these wires overcomes the dilution in the weld caused by the carbon steel. Considering the vibration and heating/cooling cycles that headers are subjected to you should seriously consider following the proper welding procedures.