US-Marine: Maybe you can contact the authors of the above addon and either ask if they can edit it into an AC556 or if you can have permission to do so.
I'm sure you are probably aware, but the AC556 is just a full-auto, short-barrel version of the Mini-14. So making the barrel shorter, removing the bipod, and maybe removing the optics and you have exactly what you requested. Shouldn't be too difficult.