I just posted about this on another forum after dealing with it less than 12 hours ago. I went to put some modernish Ultegra brakes on an 84 Bianchi bike that I am building up and realized that the brakes wouldn't work without some modification. Then I got online and found the solution that I went with - take the rear brake and use it on the front - attaching it only through the front hole of the fork and using the recessed nut inside the for crown. Then use the front brake on the rear - and just attach it with a nut. You can cut the bolt shorter if necessary - but I just left mine for now just to make sure it will work. Cost = free and no drilling holes in my vintage bike frame.