Lefy here - no major problems.
After a tactical carbine course.... I did learn a few mods that I now consider necessary:
1. Ambi safety. In the class, we were constanly going on and off safe. At the end of the day, I had a nice blister worked up from manipulating the safety with my index finger like I normally did.
2. Extended bolt release. A lefty, when doing high speed tactical mag changes, has to rotate the rifle and slam the bolt release with the left hand, removing your hand from the grip. This takes precious time, and I found the bolt release small and difficult to always strike reliably in this awkward position.
3. Tactical charging handle. This helps clear malfunctions under duress, allowing a lefty to take his right hand and charge the rifle, while still keeping a sight picture on the enemy.
I do not really see the need for the lefty-mag release.... as simply dropping your right hand back and manipulating the mag release works just fine for me. The only problem you can run into is if your mags dont drop free, high speed changes can be a drag.
If you arent interested in high-speed mag changes, or training with your rifle, then I dont think any changes are necessary to the besic A2 style rifle (with shell deflector) as it is already very lefty friendly.