Got the engine plates fitted, finally. All painted up and looking fine, the original Beezer plates have return edges that touch together along the centre line of the motor. These, as you can see, don't have these, no great loss though as it exposes the dynamo to anybody who may be interested.
The original parts list shows a spacer between the two lugs on the frame, almost definitely to stop the two frame rails being squeezed in. Probably end up cutting a short length of tube to replicate this,