Definitely a bit small, that would be more suitable for the 150. If the 180 responds like my 150 did, aim for about 9k rpm, it seems to be more reliable there than at lower rpm. The prop you will need to use depends on the nitro levels you are using and where you are, I would try something like a 16x10 or 17x8, I suspect some of the props mentioned above will be a bit heavy for the engine even with 30% fuel.

Good luck with it. BTW, what engine mount have you used and how much airframe vibration have you got? You will notice my recent post about problems with vibration in an Onyx...

James