I wound up running 3-1/2" slip-on collectors with little tabs to bolt to the header collector. Then I welded some 3-1/2" pipe from the slip-ons to a 45* bend. I added a 3-bolt flange before going into a Dr Gas X-Pipe. The X-Pipe is 3-1/2" in and 3" on the outlet. I ran the 3" pipe on the output side of the X-Pipe to a set of Ultra-Flows. I cut up the factory chrome exhaust tips that exited out through the rear valance panel of the 'Cuda and added 3" pipe adapter to the chrome tip. I exited the exhaust just before the back tires. I sent the whole system out to Jet-Hot for satin black coating. I've been happy with this setup with the exception that it's maybe a bit too quiet. I plan to reinstall the Flowmaster original 40's that I had on the 'Cuda back in the 90's. I added 1/2" quick pins that hold the tailpipe hangers to the 2 x 3 box tubing that goes from rocker panel to rocker panel in the floor just behind the front seats. When I go to the track, I slide out the quick pins and undo the 4 bolts so I can easily slide off the exhaust, drop to the ground and slide it under the trailer. I left some torque on the table because I didn't run collector extensions at the track. Engine Masters did an episode that showed pretty impressive gains by running header collector extensions. I'm getting ready to redo this setup since my new headers have 4" collectors. I'll use V-Band connectors on the header flange to exhaust system this time around. And I'll have to long transition from 4" to 3-1/2" to match the size of the X-Pipe inlet. There was a post on here about a month ago where a guy with a really nice Pro-Mod white Duster did a custom exhaust using oval stainless. It was a work of art. You should check that out for inspiration