I have a 1933 and my mag looks just like yours....maybe a little better condition. Mine does not have a grounding wire on it, and being bolted to the frame, it would seem not to need one.
To ground the mag out to kill the enginew, your mag needs to be connected to the rod for the timing. I don't know if you noticed or disconnected it, but it is at the rear of the mag. You'll want to retard the spark when cranking to start easier and avoid kickbacks. Once started and warmed up, advance the mag timing for smoother running and more power.

Hope you have fun with it.....I love mine and it runs like a top. Got two &quot;older&quot; gents in our tractor club that like it as they put lots of hours on the two their Dad owned when they were teenagers!