Guys,
I'm 6'4" 250 lbs, and have owned and driven 5 Challengers over the years. I've found the simplest solution, that makes the a very comfortable driving position is to put about 1.25 inches of spacers, (I've used all kinds of things, but large nuts work pretty good), under the front seat post and it reclines the seatback, giving you much more room between you and the steering wheel, and provides more thigh support, which I find more comfortable.
Give it a try, it may be just the ticket for ya, if not, then nothing lost. Just loosen the rear bolts some (not all the way) and remove the front bolts. Lift the front posts out of the floor and put a spacer over the posts and set them back through the floor. Climb in and see how it fits, add more, or less depending of your needs. Then just tighten up your bolts.... 1/2" deep well with a short extension.
Good luck and let me know what you think.