A friend made the bracket and fitted a modern repro switch to my wideline ES2 recently.
The "correct" norton fitting has the switch pushed off when the brake lever rises (striker plate moves back) and the spring within the switch drives the switch on when the brake is depressed (striker plate moves forward). I didn't see him do it but the switch can be dismantled and changed from push on to push off if needed, he needed to on mine.
The bracket is just a piece of flat, drilled to mount on the rear of the footpeg bolt and for the switch mounts and with a couple of bends for alignment, end on view below.
Looking at the photo i am now not sure if i have the bend in the bracket mounted the right way around, i removed it for some fine tuning, it seems to work though.