Hi Randy and all who responded,

this is exactly the information I am looking for. I was in contact with Hartzell and they gave me the info as you described - to reduce the prop to 72", and yes, it is the F7666 original prop. Unfortunately it comes with a spinner (chromed) which is a bit to large for the original cowling.
- Have you done anything with respect to clearance ?
- What is your prop clearance in inch ?
- Can you provide any performance data (e.g. climb, speed...) ?

Again, thanks to all other responses who gave me a bit more technical insight with respect to 2 and 3 blade configuration and their dis-/advantages.
Someone told me, that the 2 blade configuration has less drag and therefore is the preferred choice. I can follow your argumentation with respect to diameter and drag (as electrical engineer)  - I assume it is a bit more complex to conclude what is more efficient 2 blade with (less) drag with larger diameter or 3 blade with less diameter but more drag due to more blades ?

OK, it is an academic question but isn't that why we are doing all of this building ?

Looking forward to more interesting discussions,

thanks and take care

Peter, 360 MKII, 90%