In that case I'm thinking you've already outlined the most obvious next steps...
1. Colder plug
2. Install new head for better cooling
3. Check for air leaks after new head (i find that starter fluid is more accurate than carb cleaner when spraying for leaks)
4. Adjust main jet/needle accordingly. I know dellorto also has several needle tapers and throttle slide cutaway options, so dialing in WOT first and working backwards is probs easiest
5. I'm not sure how much airflow can get to the cylinder under those plastics, maybe you can mock up some temporary fairings with cardboard to direct more airflow and get better cooling?