Nah, sorry I counted the receivers somehow as internals as the mechanism is directly on them...
In short, the outer barrels, front ends, stocks (but I'm not sure for the stock tube) and obviously rail accessories are compatible with it.
Inner barrels, hopups, receivers, and obviously the mecanism itself aren't compatible. I don't know about pistol grips.
More info right here: http://www.redwolfairsoft.com/redwol...l?reviewID=240