Marino: I have a Norton Chopper that belonged to a friend. He used Alumalite to do the molding in of parts. She needs motor work and the back wheel off-set corrected, but it is a future project.
So on to your BSAs.
Here is what I think of as a bobber that has a good stance and the rake looks to be thought out. Link
With the oil tank and battery tray in this set up, I think a A10 or A65 motor will look in place here.
Good luck in your endeavors.