Some performance mods that are typically used in racing might help. Roller lifters and rockers to reduce power losses in the valve train for example. I don't know how useful a lightened flywheel might be, but it could help some.

There was a trick I learned about formula vee engines at one point - a groove is cut around the cam gears to allow oil an escape channel so that the pressure between the gears did not result in a power loss.

Anything that reduces power losses in the engine itself.