Too many modern mechanics on here

What you have is a fork that requires [what is referred to as] a nutted brake caliper, not a [modern style] recessed nut brake. The center fixing bolt is about 1/2" longer, and you may have a need for a curved washer on both the front and rear of your fork. Modern calipers don't usually have these.

As an alternative, you can drill out the hole in the rear of your fork. IIRC it's an 8mm hole, but I'd measure the shoulder on your recessed nut before committing to this.

To find a nutted mount caliper, come on over to C&V and post in the ISO/WTB sticky. You'll be glad you did.