You have two massive problems right off the hop (beyond the big problems like swapping drive train, wiring harness, control modules etc) and that would be the 2008 Charger and 2012 300 are two different cars from two different generations.
I'm going to assume it will be ridiculously expensive but anything can be done with enough money haha.
You will no doubt save a lot of money trading what you have in now for a used 2012 3.6l Charger.