I can shoot pistol in either hand, just better with my left. As for long arms I'm really good right handed so never saw the need to switch. I think I started out as a lefty (my mom was) but a few years of Catholic school kind of "cured" that.........I had the same problem but I’m the opposite. I can’t make shooting handguns comfortable right handed. For the rifle, I stood in the shop for a few days shouldering it from the ready whenever I thought about it. Maybe 50-100 times. It started to feel natural pretty quick. With a pistol in my right hand I feel like Don Knotts in ‘Shakiest Gun In The West’.
As Charles Shackleford once declared after a game, "right hand or left, it doesn't matter, I'm amphibious."