I haven't seen your engine and ignition module tiger, but the modules I am used to are retained by two screws that screw into threads in the cylinder casting. There is a bit of slack in the clearance holes in the laminated magnetic yoke, and you adjust the clearance between the yoke and the flywheel by moving the yoke when the screws are loose, then tightening the screws when the clearance is correct. Sometimes the holes in the yoke are actually oval to allow for this movement.
Incidentally the magnet is embedded in the flywheel, the laminated yoke does not contain a magnet. It is made of a stack of thin stampings of dead soft mild steel.
