There are actually a couple of threads on here about how to clone a Duster over to a Demon. The search function is your friend. :thumbup:
But basically, you're right. The front clip is just the fenders, hood, hood latch panel, splash apron, grill and bumpers. The frames on all of the '67-76 A-bodies are the same from the firewall forward, so there's no cutting involved on the front, just remove the body panels.
The tail panels can be purchased new now and spot welded in just like factory. If you get a later Duster though ('73-76) there are some modifications that have to be made because of some changes to the floor and quarters because of the shock mounted rear bumper. Not a big deal, but everything doesn't line up out of the box.
Here are a few of the more relevant threads, although there are definitely more.