Yes, they do, and the Mejzlik 18-6 seems to be exactly the right combination for the engine...
But for $37 plus shipping most guys will use another prop will a little less thrust and rpm...
Not a lot of difference between a 16-8 and an 18-6 except the 18-6 has more thrust because of the diameter..
My TNC tach has the little button on the side to expand the reading to within 10 rpm..[8D]
Karolh has a stock, nice and loose G23...TKG says he has one that runs even a little better..
The G23 sold for helicopters a while back had the same cylinder as the G26, same ports and timing but a little less bore..I tried one of those, got the same rpm...I think all the heli engines that Horizon sells are now G26s...