rear end depends on what you can spend on it, and how much work you are willing to do
judging by the drawing of how you want the car to look, you don't mind getting your hands dirty
so I would suggest a ford 8.8 from an exploder or so
it will require some work, but probably at half the cost of a mopar 8 3/4
if you find someone who knows how to build a good transmission the 904 will hold up to a 408, if that is what you already have anyway
plus, there is about 25 less HP of parasitic drag on a 904 compared to a 727