This is interesting. Your mounting lug appears to be on "top" of the frame rail. My lug is on bottom of the frame rail. Your switch certainly looks period.
I had wondered how much mine might have been monkeyed with, as the tab on the brake rod appear to be made from a thin slice of angle iron which was brazed onto the rod, rather than welded. The lug on the frame looked to be a stock location, but I'll have to look closer.
Yes, you have a wad of wires to jam thru that little hole in the crankcase.
Mike Sal