I had to learn how to shoot left-handed because of my left eye dominance. Also, I am unable to close my left eye by itself. I can only close my left eye when I close both of them at the same time. Shooting left-handed has worked out very well for me because it allows me to use my stronger arm to hold the rifle steady. I am a big fan of the M1A and have owned a SA NM model for eight years. I have never had a problem shooting my M1A left-handed. The ejecting brass has never hit me in the head or went down my shirt or sleeve. This is what I experienced with the M-16 in Army boot camp when I shot left-handed.
You will have no problem shooting left-handed with an M1A.