I did an L1A1 clone using a metric barrel on metric DCI receiver and replaced the gas block with an inch type. Re threaded the muzzle to RH for the flash hider and cut the groove to secure it just like the originals. The resulting firearm looks no different than if I had used an inch spec barrel unless you strip it down and look very close. This is an older picture from when flash hiders were considered "dangerous!" so it's a fake one installed. It's since been replaced with a proper item. Works like a champ. Many inch and metric parts are interchangeable and some of those that are not specifically can still be modified slightly to work.