Can anyone help me with this little problem im having?

Basicaly I have a standard ea81 flat four pushrod engine. It is going into a hovercraft where the power will be taken directally off the end of the crankshaft. The flywheel will only be used to engage the starter (wont be needing a clutch). The engine will be perminantly connected to a fan so it cant over rev. The current cast iron flywheel weighs 10kg. Is it possible to remove half of that and still expect the engine to run properly without the flyweel exploding?

Any info would be apreciated.

Dunc