Magneto Overhaul
Perspective - I'm not sure why you believe magnetos are not covered under the description "components necessary for the operation of the engine" in AD/ENG/4: the magnetos are required for the engines operation, are always included in engine overhaul manuals and supplied by the engine manufacturer.
In addition CASA regularly uses the term "components necessary for the operation of the engine" in other documents referring to engine components including the mags, carbi, turbocharger (where it comes with the engine) but not governor, alternator etc.
Even CASA would be hard pressed to argue that the mag is not required fro engine operation.