17 inch minimum. The hub design that Cass uses has stock dimensions. The rotor hub is 0.300 thick so that means the wheel mounting surface is moved outboard by 0.300 inches. So if you want the center of the wheel to be in the stock location you need 0.800 inches of offset. Obviously if you want something else then you just order what you want/need.

Cass puts a long flat section on his hub so you can use a fairly wide spacer to move the wheel location around. I designed up some 1/4 inch spacers that will be hub-centric so a person could stack them if wanted.

My Duster is more of a street/strip type of car so I'm going to run 17x6.5 wheels with 205/55-17 tires. For a B body car that was street driven I'd recommend a 17x8 wheel with a 235/55-17 tire. If it is a track car then go hog wild with whatever you can stuff under the fender.