You aren't the first to recommend staying with the stock setup. I do have the MA Stainless exhaust. I flew the machine when I first got it and it had loads of power and flew nice. I was pulling 11 degs of pitch with the stock wood blades. It just had a vibration around 1700 rpm. I'm hoping it will be fixed with the new head and parts. I found several things slightly bent and worn.

The small hub through the head that the flybar goes through had bends in the end shafts where they go in the bearings. Also the plates that hold the flybar bearings were slightly bent. That with the spindle bent. I'm hoping the rebuild will take care of all that.