I'd be looking for a Dakota. The wheelbase on a regular cab Dak is 111.9" from 1987 all the way up to '04. And from '97 to '04 you could get one with a 5.2 or 5.9 magnum. That would allow you to just fabricate body mounts to attach the unibody structure directly to the Dak frame. It would provide a little bit of body lift too. You'd probably have to section the Dak frame down so the wheelbase was 108" like the Duster though. Still, for this kind of project that shouldn't be outside of your abilities.
There's a General Lee Charger on eBay right now that was grafted onto a Durango chassis. They even used the Durango floor and firewall, I assume the Charger must have been pretty rusty as that would be a lot of work. Not to mention pretty much irreversible. If you bolt the unibody to a Dak frame it you would retain the possibility of making it a car again in the future.
Here's the ad on the Charger...
http://www.ebay.com/itm/Dodge-Charger-Charger-with-Dodge-Durango-Drivetrain-/151654145461?forcerrptr=true&hash=item234f4a9db5&item=151654145461
And below is a Duster I saw on craigslist awhile back. You can see this guy just welded brackets for leaf springs right onto the front subframe. Not sure that's a great idea for longevity...