Regardless of whether you've fitted hardened valve seats for lead free gas, these engines run best on the highest octane you can buy at the pumps. The high compression engines were spec'd for "100 octane" and there aren't many places in the world where you can find that now at the pumps.
If you habitually put "regular" gas in the tank, try a few fill ups with the best stuff. You'll likely find smoother running with no pinking, a bit more power, and surprisingly, improved mpg. If you only do a few thousand miles a year, the extra cost is out weighed by the improvements in running. In the UK I pay about twice the US price for gas and still think it's worth it!