As for an underfolder, it can be done, but it can be a pain to do it, it involves replacing the rear trunnion. Most other folder will also require you to change the rear trunnion, the Romanian side folder will go on using the original trunnion, that is what I used on my post ban SA85M, however it took some fitting with a dremel tool. If you change out your thumbhole for a pistol grip remember that you will also need to replace at least five countable factory parts with US made parts.