So how simple is it?

If you already have the airplane, you just slap on the bigger prop and go cut grass or not.

But if you haven't bought the airplane yet and you're looking for info on what size engine can be slapped into the ARF Skybolt you can't slap on the prop and tip up the tail and look. But now you got enough info to figure what'd work with the stock parts that come with that ARF.

(If you had figured you'd make any diameter prop work, you also have the info now on how much modifying you might need to do.)