Recessed nuts... No Problem!This is a 1971 Motobecane "Le Champion" with a Tektro 521-AG FRONT brake caliper (the one with a longer bolt) mounted here on the rear brake bridge. Those are simple concave washers which would also be used on this bike for any nutted brake as well. The bolts are the same diameter for either style of brake. I just used a simple stainless steel metric "acorn" nut here in place of the original recessed nut. A simple hex nut would suffice, but I love stainless steel and this style of nut keeps the bolt end threads nice and clean.
For the front caliper, I inserted the shorter bolt of the REAR caliper through the front side of the fork crown and then tightened down the recessed nut which was slid up "INSIDE" the fork crown (as in, inside the steering tube) and with the bolt passing only through the front side of the crown. You can reach right through the empty rear hole at the rear of the crown with an Allen wrench to tighten it down. Depending on the thickness of your fork crown, you may need to just add a spacer (or a simple washer or two) to take up any slack if the bolt feels at all loose.
... No drilling required.