I see this reply is a few months late. As far as I know, the Sloper was originally fitted with a Lucas Model MDI mag-gen. This had an on-board regulator. I see from your photos that you have a Lucas MO1 mag-gen. This is a slightly newer, more popular mag-gen and is directly interchangable. It does not have a built in regulator though. Of the many bikes fitted with the Lucas MO1, I would select the M20 as a base. You should easily get a regulator for an M20, if not original, then a modern electronic one. You can then use the M20 wiring diagram which is very basic.