If you're going to be running track days with a big B body car then stepping up to a 13 inch kit is smart. You'll have better choices with 17 inch rims and the bigger rotors will work better than the 11.75 inch stuff.

DoctorDiff sells a 14 inch brake kit using new Charger rotors and Viper calipers if you're willing to run 18 inch rims. I'll send you a PM with info on the used Viper calipers that I have for sale.

I'd recommend a rear disc kit from DoctorDiff rather than trying to use the Viper setup out back. The Viper uses two calipers per wheel in the rear which requires double fabrication. Also, the Viper bolt pattern is 6x4.50 so the stock rotors don't fit on a 8.75 rearend. By the time you fabricate the custom mounts and get new rotors built you'll have a bunch of money invested.