That's Kenny Wayne Shepard's Duster. Built by Ted Moser, not Hotchkis. It actually uses few different Magnumforce suspension parts. It has 18's in the front and 19's in the back, not 20's.
http://www.hotrod.com/cars/featured/0803phr-kenny-wayne-shepherds-1970-plymouth-duster/
18's are easy, and better for the "pro-touring" look because you can run extra backspace to fit larger tires up front, with 17's you still have to worry about outer tie rod end interference. With 18's the outer tie rod end fits inside the lip of the rim. Better performance tire selection in 18" as well, although pretty much anything that comes in 17" is still light years better than a BFG T/A hockey puck.
The trick to larger diameter rims is getting the ride height right. I think 20's can be done right, but at that point you're losing handling capabilities to the weight of the rim and sacrificing ride quality with the super short sidewalls. Plus the car has to sit VERY low for 20's to look right.
18x9's with 275/35/18's up front and 18x10's with 295/35/18's on my "duster".