While doing some research on upgrades for marui/marui based shotgun I learned that they are derived from maruzen's design (on the exterior) and that it is a fairly easy mod to slap on a maruzen full stock on them (870).
Maybe that could be of help Max?
EDIT: found the page, I was at work this morning and didn't have it on hand, it's from france airsoft so if any of you need help translating stuff I'd be more than happy to help out! (5th post):
http://www.france-airsoft.fr/forum/l...hp/t32828.html