Counter rotating a reed valve 2 stroke is easy, just set the timing 28 degrees on the other side of TDC...
6700 rpm with a 22-10 is disappointing ? Get real, it's only a 50
And..All 22-10 props are NOT created equal..I have 2 22-10s here I guarantee will turn less than that, a PK and an MSC...Either will load an engine down way more than a Mejzlik, Bolly, or APC...Or whatever other prop is out there...Not all props are pitched as advertised