Go to this site for info and I have used lots of there stuff including having him make header flanges for various cylinder heads---they are located in Fargo ND---he used to do race aircraft stuff
Stainless Headers Mfg., Inc. fabricates custom headers in stainless and mild steel
Also for some other stuff
www.coneeng.com for collecters and handing construction tools. I like these collectors for lots of exhaust systems where they don't have to come apart often for tuning etc to change lengths of tubes