Bob is absolutely right.
We cannot bring a full scale airplane with us for competition, even if one existed. A person who is an 'Expert Authority' of a particular airplane is not an acceptable form of proof of scale either. So what can you do?
The AMA rules gives us 3 choices, 3-views, photos, or a plastic model. If you choose 3-views, what source? If you were to research and collect 3-views from 10 different (acceptable) sources, and compared them, chances are, the'll all have differences. If you choose photos, what if you are modeling a plane that no longer exists, and photos are not sufficient to adequately prove scale? Reading about the restoration of full scale airplanes, there are times when even factory drawings do not match a specific airframe. As for a 1/72 scale model not being large enough, many 3 views that meet the AMA criteria for being acceptable, are drawn at 1/72 scale too. Of course, as a competitor who is trying to win, you will want to select the best documentation you can to provide as proof of scale. And if you want to score well, it would probably be best to select your documentation first, then build your model to match your documentation. After all, judges have no other source of information about a model other than the documentation provided by the modeler.

Scale competition is an aspect of the hobby I want to explore. I have not competed, and have seen only a few examples of documentation packs. I am curious, is anyone aware of someone who has used a plastic model for proof of scale and won a major AMA scale event?

Scott