Hi again sorry about the delay in replying, no there doesn't seem to be a spec for any part of the Model Z / Wessex bikes. I have managed to track down a couple of photographs which show something of the mag dynamo, unfortunately from strange angles, and they seem to show what looks like either the MN2 or MOL model which I can only track down as a single cylinder version. I think I am going to have to stick to my MN magneto and keep looking for the correct Cam end cover to replace my damaged one.
Thanks for your help on this
Chris