It will be interesting to see how you get on with this. Tyor could well be right, he has had good success with his NGH 38 on that propellor. I could only get about 6700 rpm on mine. I went to a 2-blade XOAR and did advance the timing a little. I was able to get about 7000 rpm. I also changed the position of my valve timing gear. I had previously retarded it, and although the engine ran far smoother it did loose a lot of rpm. I put it back to the factory position and this restored my rpm considerably.
I know my inaccurate "tinkering" will probably frustrate some of the more learned and experienced 4-stroke gas engine experts. I should buy a timing gauge and do things properly aye!
Good luck and please keep us posted with your progress!
Alf