Can you relay what aspect seemed to be "extra strength"? If it's about the amount of material beyond the axle slot or running down to the hanger then simple viewing might give you a good idea as to current drop outs' strengths WRT the old Ritchey's. I suppose it could be that they were slightly thicker then average, but would be surprised if this was it. Perhaps the drop outs were cold fordged, although after going through the thermal treatment, that we usually call brazing, I question what strength advantage would survive building the frame.

Generally a drop out is chosen for the slot type, the joining to the stays design, the hanger length and shape, the angle between the chain and seat tabs/plugs/sockets, eyelets. Strength isn't even on my list. Andy