Harvey is a bit of a conundrum when it comes to position. You would think he was a natural loose, and the U19 coaching staff have tried him there, but it wasn't a great success. Perhaps a year on and a bit more experience under his belt would allow him to make the transition. In the meantime he is a strong player, difficult to stop near the line, hard in the tackle and with good handling so yes, he could probably fill in for a number of positions. Plus he can kick goals and is as cool as a cucumber under pressure.
I am not convinced of Moran or Johnson I am afraid, and Prell is still just a vague possibility as we have not heard or seen of him for quite some time.