On the round track cars with limited ground clearance under the rocker panels, we used to split a piece of 2" exhaust tubing down the middle and splice in a TIG welded 3" wide piece of 16 gauge flat stock top and bottom. It ended up making an oval exhaust pipe that transitioned to the header collectors with a cone shaped adapter, which was also fabricated in the shop.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!