I drilled and tapped the holes for the plate to hold my pickup sensor in about the only place possible, there isn't much metal down there. If you do decide to try to fabricate a bracket to hold the mag, keep in mind that you'll have to locate the mag in the same place that its mounted in the saw. If you plan on centering the mag on the cylinder like most engines, you'll have to get a different flywheel or remove the keyway from the stock one and set the timing yourself. Too much trouble for me.
The C-H coversion is the easiest. Do you already have an ignition? Saw out the center section of your flywheel, turn it the same diameter as your prop hub, and mount the magnet in it.