As pointed out above, the 1911 is already a very ambidextrous design. You really need only an ambi safety, as the slide stop and mag release can be operated with either hand. I know two people who use ambi mag releases, and they're both right-handed - they find operating the catch with their trigger finger is easier/better than with the thumb. To lock the slide back, I push up on the bottom of the slide stop with the side of my trigger finger; it's a kind of an unusual movement, but one that is easily developed. I have found some guns are very difficult to drop from slide-lock using the tip of the finger, so I wrap my right hand up under the butt (kind of a follow-through after the reload), and release it with the tips of two fingers of my right hand. I've seen some guys try to get along without an ambi safety, using their left thumb on the standard safety, but that seems to slow if done after the draw, and dangerous if done before.