What's the best way to increase power on a naturally aspirated A70?

I've had my A70 Supra for about a year now and I'm getting some decent performance out of it, but I know there's more to be had. I've been looking into mods that can increase power without resorting to a turbo or supercharger, and I'd love to hear from others who have successfully increased power on their naturally aspirated A70s.