I took my son and friends out to shoot the other day and started his friends, who had never shot a gun, off on my 870 synthetic pump. One missed every target, until he told me that he sees better with his left eye althought he writes and does most things with his right hand. I had him switch to shooting left handed and he started hitting about 40% (this was 16 yard trap). I then let him shoot my right handed Citori o/u, which has a pretty good right hand palm swell and he was hitting close to 60% and having a ball. I do not think the type of gun, right handed ejecting pump vs. rear ejecting break action o/u was so much the difference than he was warming up to shooting. Perhaps the Citori is a bit more refined than a $400 pump.
I think it a big mistake to try to make a lefty shoot right handed.