The stock headers can be effectively repaired so they don't recrack. Proper preparation and welding process are a must for a long lasting repair. The gusset works to avoid recracking.
The area to be welded should be bead blasted and the cracks stop drilled. The header should be bolted to a scrap head to avoid warpage. You need to have the header TIG welded using Stainless steel filler rod. These headers are made from a low grade magnetic stainless steel. If you try MIG welding them you'll just make a temporary fix and wonder why it didn't last.