Corsair used a 18 cylinder radial Pratt & whitney Double Wasp. It used a ring type header to collect the exhaust, which exited out 2 header tubes on both sides the cowl at 4 o'clock and 8 o'clock positions.
I have seen the other headers for the war birds that had V-12s in them You can get something similar to the Corsair but it`s for the radial engines. The header wraps around the engine a lot like the big ones do, but you still have to add collectors and exhaust headers.
Good luck.