Take it apart, take the crank out, Push the bearings out or cover them with some duct tape...cut or grind off all the extra casting until you just have the round part of the case...Make a flat plate that uses the case bolts to hold it together..You can drill out the case bolts with a .194 drill and use 10-32 bolts all the way through the new back plate to hold it together..cut off the rear straight part of the crank a little above flush with the rear crank seal...Re install the crank..Make a new prop hub with a magnet in it and a bracket for a Hall sensor for the CD ignition....Picture is a 4.2 Sachs chainsaw conversion, same idea except the ignition is inside the mount...