Is G-23 and G-38 mount bolt pattern the same?
Yes - Don't run a G38 at 9000 rpm or even near it. It won't thank you. Best rpm range from my experience with them is 7000-7800 on the ground (I don't often measure it in the air. I wonder how Zenoah does it?) The 18x6-10 is a good prop for the G38 but I have found that an 18x10 pulls better once they are run in.
Gerry Rosebery