It would be pretty easy to make this rack work by bending one of the forward stays to fit the caliper bolt. FWIW, the forward stay on a bike rack carries very little load.

https://ecom1.planetbike.com/4001.html

There were Blackburn racks that had the caliper mounting point (have one on a bike). You might check used bike part emporiums, eBay, etc.

I suspect that your rear dropouts could be drilled and tapped for the heavily loaded vertical rack members. Perhaps that small hole forward of the axle was intended for rack stays?