What fuel is best?

As mentioned above. You should be fine on 93 for the trip. As said above, if it pings, something is mis-adjusted. Check the idle w a vacuum gauge, maybe a compression test. If it was all good, I wouldn't hesitate to drive a stocker across the country.

If it's high mileage, you could try the old water trick - dribble water down the carb, as much as it will take without stalling, while holding the throttle around 2200-2700 or higher. Should be fully warmed up first. It will pop and miss, but also steam the carbon out a bit. This can be a tricky, or risky procedure if you've never done it before.