If it doesn't work, then it's only because Ruger uses a non standard button, all internal features of the latch will be standard. So if that is the case - non standard button - spend $7 and replace the Ruger latch with a standard latch with a standard button and you'll be in business.
My thoughts exactly, modify or replace. I just could not remember if the ar556 has a thicker upper like the dpms where the bad lever does not have any room to operate because of the recess the bolt catch slides into when depressed. I also cannot remember if the ar556 has a threaded bolt for the bolt catch to attach with like the lr308 pattern lowers or if its a normal rollpin per milspec and seen on 95% of ar rifles and pistols. Those would be the only reason other than a ruger specific bolt catch that it would not work. Seeings how they used a funky barrel nut, I would expect differences elsewhere.Like mentioned, it should. If not replace the release or modify the lever. It just clamps onto the paddle.