You should really turn down the taper slightly to match the puch flywheel (the derbi crank is bigger) otherwise you risk messing up the woodruff cutout on the flywheel when turning serious rpms. technically only about 40% of the taper is in contact with the crank.
That being said I used a za50 powerdynamo on my pyramid reed bike after I used lapping compound and the flywheel puller attached to a drill.