Richard Gentil - CEO of Naples Air Center, where I did the IR. He'll tell it like it is.
His (or rather, his wife's) advice to me was that to do an IR in two weeks I did not need a visa, but if I stayed more than a month doing flying training, I definitely would.
That may have changed recently. Best suggestion I can make, unless Richard pops up with the answer, is to have a good browse of the web.
Calling the US Embassy is mostly a waste of time. I've done it a few times, and found it very frustrating. I didn't get the information I wanted.
Sorry, and all that.