Hello, Wad:
Good question. The governing body had been working on what is correct and what isn't, but unfortunately we let things slide as we got into fall and people started gearing up for winter. As you can imagine, it's a slow process even under the best of conditions, since so many firearms from this period could be locally made.
Just remember that what we're trying to create is a group with an emphasis on historical accuracy. Not one hundred percent, but better than the average rendezvous or some of the cowboy shoots, where you can see a wide range of non-PC outfits. Think Level-One NCOWS, or what the folks at GAF are trying to accomplish.
You're right in that your rifle is shorter than the norm, but the basic silhouette is that of a Kentucky (or Pennsylvania, the difference is slight). If you showed up at an American Plainsmen Society match or encampment with it, I'd allow it. Especially for a woman or youngster.
What we're trying to stay away from is the Thompson Center or CVA or Cabela's Hawkens, which are no closer to an actual Hawkens rifle than a Henry Big Boy is to an original Henry. The Lyman Great Plains rifle or the Pedersoli Kentucky rifles are acceptable; the Traditions Kentucky rifle with its brass band connecting a two-piece stock isn't.
I'll also add that the governing body is in agreement that we need to give new members one year to get their basic outfit together. Hopefully within the next month or so we can have a list of correct guns available and posted.