Sounds stupid....but,

If detonation is the problem, get a water injector kit and it will go away.

I used water injection on a 11:1 comp. 429 from a '72 t'bird to stop pinging and still was able to use regular-low octane fuel. It was in a '56 FORD pickup and pulled a trailer too. Just check the water level everytime you fuel. Worked well.