Here is a Fairbanks Morse service bulletin for the American Bosch AB33 installed on the Model Z engines to help keep yours alive and well.
Here is some more information that came with your new Fairbanks Morse Z engine back in the day.
Your magneto is probably out of warranty.
Do not be afraid to remove the interrupter, that is what the strange looking wrench is for. Mostly, be careful that the key in the interupter is properly indexed in the armature keyway before tightening the center screw. Be sure the points are smooth and shiny, and the rocker pivot pin is not rusted. It must be lubricated and rotating freely in the phenolic bushing in the interupter base. If there is rust on the pin, polish it smooth with crocus cloth and smear some grease on it before reassembly. Point clearance is important, if not near .015", the mag will not fire. The special magneto wrench came with your new magneto and is nearly always gone but they do appear at swapmeets. They are worth picking up and keeping handy during the shows.
Brake or electric motor cleaner works well for cleaning the brushholder. Sometimes after running over time oil from the engine will get inside the points cover and on the points causing failure. If your distributor/ignition wrenches do not seem to fit it is because despite being made in Springfield, Mass. many of the fasteners are metric. Usually the points screw and locknut are 4 or 5MM across the hex and very hard to get at. Often it is easier to take the points out, make the adjustment, reinstall then check clearance.