I did a similar thing with a Road Runner. I would start with a Super Bee. Why? Because its what the A12 car was before they added the A12 parts. So, you will already get the heavy duty suspension, 3" drum brakes, and other performance chassy parts, as well as the interior and trim.

The parts to make a good clone or replica, IMO, are the dana, 6pack setup, hood, pins and air cleaner. You can get by with the standard 23 spline transmission if you are going with a mild build on the 440. You'll also need a 3 speed wiper motor. Those are the big ticket items I can see. And they are all avaialble aftermarket.

I see "Six Bbl" clones on ebay that are just road runners with a fiber glass hood. If your going to make the effort, then go all the way.