I myself would drill it out and tap a larger size (either metric or SAE). The use of a Heli Coil or the like should be used as a last resort as you need to drill a much larger hole for the Heli Coil itself. Don't get me wrong but Heli Coils have their place and time. Which hole exactly did you pull the threads out of, you say "into on the lower end" ...be more specific...Cylinder stud, case bolt??????
If the bolt you are talking about is the #6 bolt at the bottom of the case, directly below the coil/magnet, I'd drill all the way through with any of the following drills...6mm, 15/64 or a "B" drill bit and insert a bolt long enough to install a locking nut on the other side. If this is the one..it's a piece of cake.