Rob,
Rather than recommend my favourite engine, let's look at the model itself.
Hangar 9 specifies a flying weight of 8.25 to 9.5lb and recommends a .60 - .76 Two stroke or a .91 to 1.00 four stroke for that model. That information suggests that the model will balance with an engine weight of approximately 23 oz, give or take a couple.
A Saito 1.00 (21 oz) fits into this band and so does the OS .91 (24 oz). Both these engines, with this weight range, will provide adequate (for scale model flying) but not sparkling performance. For example, I doubt that the power will be sufficient with these engines to do large loops or any routine requiring a long upline.
If you are not looking at doing aerobatics or expecting lots of speed and are just looking at flying circuits, a few rolls and the odd small loop, the Saito 1.00 or the OS .91 will suffice. You can skip to the end of the post now...
If you want more than adequate performance, you have a couple of options.
Going with an traditional "big block" 1.20 engine like an OS Surpass, Magnum or other 32 plus ounce engine will probably require additional weight to be placed in the tail to balance the model. This additional weight may mitigate any performance increase the additional power may promise. This option is therefore not recommended.
A Saito 1.25 (25 oz) does not weigh much more than the .91/1.00 engines and is still in the acceptable weight band, yet it should get closer to providing enough power for some reasonable aerobatics. It should be very user friendly just like the OS and Saito engines mentioned above.
For a very high level of performance, the YS 1.10 (27 oz) is the ticket. Power-wise, it will pound any other brand of four-stroke up to 1.50 into the dust and, contrary to the naysayers' assurances, is very economical on fuel. It's only a couple of ounces outside the band, so it could possibly be accommodated and balance achieved by moving the battery and/or receiver around a little. Once set in accordance with instructions, it should be a set-and-forget engine like the others mentioned. It doesn't care where the tank is situated either - a huge bonus for an ARF Warbird application.
Ain't it great to have choices...