The Sweptline that everyone wants is the Sports Package with the 426 Wedge.

To answer a year-old post, the difference from an H-code Duster is that the Duster DOES have more than an appearance package and it was originally a neat and hot car, so if one restores it it will be in fact a real one, not a clone or a look-alike. In the world of collectors it makes all the difference, and as long as there is someone out there willing to pay a lot more for a restored H-code Duster than a re-engined slant six Duster, it will mean something.
And I'm sorry, local dude, but a 318 powered 1974 Road Runner is not a muscle car, even though it carries the name.
R.