An m20 flywheel is well worth it, they can be lightened alot, mine weighs 9 pounds, as for the starter, you can have the flywheel machined to accept an m42 starter ring or put an m20 starter gear on your m42 starter. As for an m40 flywheel, I do not know if it will fit. On my other car, I have an M42 non ac flywheel that has been lightened to 17 lbs and it is a very nice set-up.