If you can find one labeled as an SAR-4800, it should be good to go. If it's an SAR-48, it's banned by name. They pop up on GB once in a while.Didn't Springfield market a .223 FAL a long time ago? I wonder if that would be exempt (ala non-5.56/.223 ARs)?
Someone else also made some 5.56 builds, but I don't know if they're any good.