I've read recommendations that you that the results from spocalc and round down to the next smaller size. Sheldon Brown recommended rounding up. I guess it's not that precise.

Be sure to let us know how these turn out. I have a set of old Lambert hubs which were the same dimension as Campy Hi-Flanges. I plan to build these up with wide, strong rims as an alternative for the tubulars and Mavic Open Pro wheels I have now.