What I would do with the concept, as shown in this link, is the following:
Exterior: Take the Challenger badges off of the rear quarters and put ONE across the rear end. Add raised chrome badges to read: "6.1 HEMI" to the hood scoop and remove the decal version.
Interior: Flatten-out the center console/shifter area. Make the gauges the same size (it appears that the cluster goes from large to small, as it moves left to right). Offer a Hurst shifter. Offer an automatic in SRT8 trim that offers the same general performance perameters (gearing). Keep the chrome/aluminum... heck, add some more! Leave the seats (need the embroidery), etc. as is.
Engine: 392 or boost the 6.1 rating to 475 or above via factory mods (the GT500 is gonna pump 475 at least, and likely weigh less than the Challenger). If Dodge is gonna do this, they need to produce a car so bad ass that the GT500 or future Camaro won't even bother lining up against it. You know, a car that'll out drag damn near anything under $100,000. With 500 ponies, that shouldn't be an issue. They did it in the 70s. Do it in the 00s.
Offer it in a few basic colors (silver, black, etc.) and a few retro colors (plum crazy, etc.). Painted calipers too.
I think I'll take mine, black on black. With the high polished alloy wheels, red calipers... thank you.
Add in some customized black floormats with "Hemi Challenger" embroidered in BIG SILVER letters, and I'll forever hold my peace.