The 1320 is an option package on the R/T Scat pack. Go to dodge.com and go to "build and price". It seems the 1320 package is harder to find on dealer lots.

73 Challenger 340(416),E-heads, 727, 3.23 SG
2015 Challenger R/T classic B5, wife's car
2010 Ram 3500 Crew Cab SLT dually 4X4
2016 Challenger Hellcat Redline Red A8