I own such a monster, really crazy torque...i love it...SEM Ignition is a problem to find, if it is broken look for NOS parts or replace the complete ignition with the Bosch ignition system inclusive flywheel. For the bearing on clutch-side shoud be a workaround with a self-made-washer.
I fixed one up for my cousin last year. Had to wire in a new capacitor. Used frogies instructions to do it. Swear I bought the last set of stihl seals for it in existence. Ran great with the ignition fixed. Begged my cousin just to dump it. Thankfully he listened and sold it off. Parts were hard to find and pretty expensive for what they were.