[Jamo]

I know you're talking about SPFs or ERAs, but you might want to chat with Gerry Hawkridge at Hawk Cars, who finishes up Kirkhams and their own chassis for use in Europe.

For such speeds (which I agree with others...tough in these things), and barring any thoughts of a Daytona Coupe, you might want to think about a LeMans top equipped Cobra, and think about a rear-exhaust setup.