I would run the minimum amount of oil in the engine and a thin grade like 0w-16 or 0w-20 if it's OK in your engine. Usually going down one grade in oil weight is OK.
Thinner fluid in the differentials should help too. I'd be tempted to go really thin and change back to normal fluid after the event.
You could cover the front of the car when it's not moving to hold the heat in. Or a full car cover. Or just insulate the engine and hood. Even just parking out of any wind could help.
Practicing different driving techniques in the car before the event will help a lot.
Any braking should be avoided. Friction or engine. Can the car coast in neutral?
What part of Finland is the competition? I've enjoyed driving all over Finland.
Since it's on public roads, can you have a friend with a big van drive in front of you?
