I've asked the same question myself. I think you're okay with that.
If that was a shotgun, it would be perfectly legal since it would be at least 26in in total length.
So why not a CF or rimfire rifle?
Something you could also do is put a Choate side-folder on it, only using the pistol grip function! But also having the f-stock for extra stability if it was ever wanted, too.
But if you indeed put a folding stock on an Encore or Contender frame, any bbl less than 16in would then be illegal.