The adapter pictured is called Brake Therapy, though far as im aware that is not original.
I think this one requires you to drill a hole through the dropout, which isnt as bad as it sounds or difficult, but there are other options, probably more in keeping if you want to try to stick to originality.
This is one of the modern options, should you want different brakes
Hope did a hub mounted caliper for non disc frames, one of the Closed 2 calipers(numbered No2), but is reliant on being used with hope hubs that use a solid axle. All the parts to adapt one of the hubs is available from me, or others here. The brake itself you'll need to find. Again im sure you can source that here.