Here in Hastings, MI we have the Barry Roubaix, Noted as the worlds largest gravel road race with multiple course option built in. A 22 mile, 36 mile, 62 mile and 100 mile option. With the rising popularity of this race/course (sold out at 3500 riders this year). I think this would be a prime course to mirror your next world after.
The BRX course could be expanded to include Yankee Springs as well.