Thankyou so much for the reminder! I've been so busy with getting the engine to fit that I hadn't thought ahead to fitting a skirt guard. Amongst all my vintage treasures I did at one time have a rear mudguard that had been drilled to fit a skirt guard, but unfortunately it had been 'bobbed' by some horrid little vandal so I couldn't use it.
Trust me to be attempting to break new ground with this conversion, but as you say it should result in a strong and tidy motorised bicycle once I have it completed. I do own a digital camera so once I have the frame properly sorted out I will take some pictures.