There's a ground braid that exits next to the spark plug cap. I've connected the strap to a convenient bolt on top of the head.
The manual from BME says that the ground strap "must be attached to the base of the spark plug."
I can't see how that would be possible, but I'd hate to blow the ignition if I'm wrong.
Here's a a pic of the mounted engine.
Have I set this up correctly?