There's a reason for the Quad exhaust especially with super high horse Hemi's.It decreases the back pressure that a pair of single pipes won't handle, a high horse hemi has to breathe and you run too large of a diameter single exhaust sytem you lose back pressure, so going with a quad set-up balances and equalizes the pressure put out by the engine, you would know this if you had too run an exhaust on a 700+ horsepower engine. Just thought I would mention this, also look at the exhaust real close on the Silver Bullitt 67 Plymouth GTX of Jimmy Addison, same set up. I think that Challenger looks tough as hell.
Dave