All of those Austro-Daimler and Puch 531 frames built in Graz are silver-brazed. They are genuinely lovely bikes.
I rescued my long-lost ‘76 Puch Royal X last year, same frame as the Royal Force and comparable to the earlier matte black Vent Noir. Just for giggles, I’ll note that my 59.5 cm to top with a 57.5 cm top tube is 73-degrees parallel with 43.5 cm chainstays and 51-ish mm rake for 52 mm trail on 27 x 1 1/4 Paselas.