Sean,

It is often easier to follow a few simple rules or an example like you have found than it is to read many opinions on what is the best way to go.

The example you found on the Ultrafly A/30/29 sounds reasonable. Another suggestion is to look for a review of a similar size plane and see how it was powered. A quick e-mail to the vendor you plan to buy the motor from is a good idea if you are not confident in your choice.

Use the watts per pound rule of thumb either for the motor power class selection or as a sanity check. Your model weighs 22oz or 1.4lbs. A P-51 should have at least 100 watts per pound of power to fly aerobatics. This means that your motor should be able to handle 100 * 1.4 or 140 watts. There are many, many, 150 watt power systems on the market for you to choose from.

Good luck!