Here is what I did. It would work much easier if you have a split cowl. With this setup I was always below 300*F no matter how long I ran at WOT even on the ground. All bottom louvers were opened up (not the top) and on the other stock opening I put a low pressure lip.
Oh, all other open areas were sealed off on the motor box. The air came in the top and only had one way to go (by the cylinders) to exit out the bottom
Don't laugh at my looongg stand-offs, they did work well but allowed a fair amount of vibration so I had to tie them together