Re: A Mixte framed motorised bicycle for a lady.
I agree that your engine fits the frame so nicely with your alteration. Looks like it was made that way as a commercial motor bicycle. A cylindrical tank would be just right. Looking forward to the finished bike, as I'm sure you are as well...
For the skirt guards you could drill holes along the edge of the fenders for lacing cord or maybe there is a way to use spokes from a spare wheel. At the hub you could have a disc shape the cord gets laced to or the spokes fit in and which is held in place by the axle nut. That piece could be kind of like a washer... maybe the end section of a tin can with the lid in place and a lip of the can perhaps an inch or so with holes drilled into the lip. At the center of the lid (still attached), it could be drilled out to fit over the axle. Just a thought.
Someday when I grow up I will probably lose interest in toys with wheels, but until then...