You need not limit yourself to nutted calipers. Should you find a nice period correct pair with recessed bolts, they can be used as well, no drilling required.

The front caliper goes on the rear, where it is mounted with a normal nut, ring and spacers. The rear caliper goes on the fork, using a 'coupling nut' and is tightened with a bolt. Like this:


(picture respectfully lifted from m-gineering.nl, where you'll find the instructions - use Google translate if you don't read Dutch)

Used this a couple of weeks ago on my Bovid Blues Beater, and was quite pleased with the results.

EDIT: it seems the forum software doesn't accept links to http sites. Remove the "s" manually from the url for the m-gineering website and it will work.