Ok, could not get a clear answer from falfiles.com so here we go... I have a Aussie L1A1 lower and a Imbrel Brazilian upper imported by CAI. It has the thumb hole stock on it (thanks to clinton). I know the 7 US parts to put on it. Gas Piston Trigger Hammer Sear Buttstock Pistol Grip Forearm The upper is a metric, I believe the lower is an inch. Is there a difference in the stocks? Can I just put a US made furniture set on it or do I need half metric half inch?