I can tell you they are 100% sick. And the only reason to do it at all is looks. Black Plummer’s pipe can be sanded with a flap wheel to be just the right size to hammer up into most stock forks. Hammer the ends flat , drill a hole and make a slit for the axle, then hammer them in, line everything up good so the axle is both level and straight, and weld around the joint!
I should add, the black Plummer’s pipe worked for these kreidler forks and some maxi forks just fine and easy. No clue if it’s good for a Vespa. (edited)