If it's a Ruger AC-556, the chances are very good, particularly if the *juveniles not identified due to their tender ages* are sons of a local cop or former cop. But I'm aware of at least one Title II dealer in Montana, and I'd be much more inclined to bet that a Montana sheriff's department and newspaper would get it right than their corresponding counterparts in New York or Los Angeles.
The full-auto Ruger AC-556 version of the Mini-14 goes for around $6000 from one NFA dealer in Maine I'm aware of, pricey, but not as steep as a more collectable early Thompson.
There used to be dozens of books that would tell you what you needed to do.
I had an uncle that was a gunsmith and machinist and he thought the various conversions were half-assed (for whatever reason) hed always say that the conversion was a good way to F-up a perfectly good rifle. But I doubt that ever stopped anyone from doing it.