3.6 in A-body

Hi Everyone, I'm in the early planning stages to put the 3.6L in my '64 Dart Conv. As I see (what I believe to be) the outrageous prices for an 8 3/4" and now even the 8 1/4", I'm wondering if a better option may be to retro-fit the rear end of from a Challenger/Charger, so as to bring the entire drive train over from a donor junkyard car. i understand that's going to require a decent amount of modification, but hey, a friend put a jaguar rear suspension in a '31 Chevy roadster, so it's certainly doable. Thoughts?