I think that it might be quite a good fight. Willard was certainly durable and strong but Botha I feel may well have a substantial technical edge since Jess' technique was, um, not great. I'd take Botha on points.
Francois was a cunning specimen in his prime. Willard would be putty in his hands, both literally and figuratively. Jess or Fred.
Willard UD in a 10-12 round match, WIlalrd via TKO 15 or more rounds. Willard looked better than Jack Johnson did vs. Moran. Moran had a hard time getting into range. Botha would have the same problem