Hi Nigel and ALL,
To the best of my knowledge, the competition magnetos are built from higher quality materials as well as the differences noted here already,
The method of fixing the drive shaft to the armature is different or beefed up ?? its not a steel shaft just pressed throught the brass end piece as on the "ordinary" mag
On the ZB 34 I am working on it has a Wader magdyno, this has a different end at the points side which has a brass points plate and ring cam as opposed to the face cam on the normal magdyno, so its got a different type armature as well. (I havnt looked inside this mag tho)
HTH
John O R