Hey geminiviper, I'm an older guy, i've done a few projects like this, and offer this advice.
Take the path of least resistance, the task is pretty big, lots and I mean lots of guys with great intentions start a big project only to find it is more.. in cost and time than they can manage. A mostly stock 440 4bl 1970 Challenger, is very very cool, a 6.1 has an added level of interest, but will costs lots and lots more in time and money. Plus you'll find less people who can help. Consider taking an easier victory this time around, after a couple under your belt, step it up. You won't likely lose money on a completed stock 70 Challenger 440 4bl project that gets completed, but will lose your a__ on any uncompleted project. Good luck.