318 to 440 Swap

Not sure about Darts specifically but through my research.

You'll need mostly this:
- motor mounts (Schumacher creative services has them)
- new headers (TTI or SCS | Schumacher creative services has them)
- larger torsion bars will be helpful
- Atleast an 8 1/4 rear end, but you'll want to aim for 8 3/4
- Atleast get disc brakes on your front
- Going 8 3/4 will most likely swap you to BBP wheels
- Need a drive shaft with the correct fitment for a 727

Tons of info relating to darts here: http://www.bigblockdart.com/techpages/techindex.shtml

My thread that has pretty much all the answers of what you'll need:
http://www.forabodiesonly.com/mopar/showthread.php?t=328604
My thread is realting to '74 duster so you might need a few other odds and ends for your dart.

I've been told the entire swap can be had for < 1500 which for power to cubic dollars, isn't too bad.

Good luck!