Usually the best range in an aircraft with constant speed prop is achieved by flying with RPM set at some low value (2000-2200 rpm), full throtle (or maximum continuous manifold pressure, but it's best to fly at altitudes where full throttle gives you max. continuous MP or less to reduce pumping losses) and mixture up to 30-40°F LOP.
PM if you need max. continuous MAP for given RPM for Lyco IO-360.