My first build was on a Stag lefty upper. Put an ambi safety and a Norgon ambi mag release on the lower. It's my bench gun and I'm really happy with it. All my builds since have been right handed uppers with an ambi safety and I'm totally satisfied with them. FYI my lefty upper barrel has an ambi bolt extension. I've heard people say it's unnecessary but can't say it's a fact.