Oilman, talk to Ozvenom (Scotty Hampson) Venom Custom Fabrications in Meadowbrook Brisbane. He's made pipes for all sorts of cobras including Digby Cookes Stainless units on his Robnell.
Remember they will be like 2 very long BBQ HOT plates when those gases are pumping through em and you will need some of this to remove your skin once it bites you.
Selleys BBQ Tough Clean - BBQ Cleaning | Selleys Australia
Also remember it will turn goldish yellow from the headers back like a fire place flute.
Hope he can help. Spookypt.