Just put together a rifle using Aero M4E1 (non-ambi) receivers. Though I'm a LH shooter and definitely prefer ambi controls, I've avoided manufactured ambi receivers only because there was no standard design. Not opposed to using them in the future though; in fact I nearly got an LMT recently. Up to this point it was simpler to get standard receivers on my rifles, then add an ambi selector (Radian, B.A.D.), and a Troy ambi mag catch. Don't bother with the bolt catch.