Standard engine goes easy to 8000rpm. What you have to do: balancing crank and flywheel and pulley.
To rev higher, like andyb said. Lighter valvetrain is the best way. Look on the followers i had for my project. 160gr. less only in the cylinderhead.
Its not a problem to rev near 10000rpm if you know what you have to do.
But to make safe, you need a lot of money only for the engine.