Richard I don't know about SW guns if they had a cast off for right handed shooters built in. Most of these guns I think are fairly neutral but that is definitely an important question. Personally I think gunfit is important if you have both eyes or only one. Not certain how cost effective to buy cheaper gun and then spend extra to steam fit the stock. Maybe able to find one already bent lefty. Here is one that is Cast On for lefty made by CZ.
http://cz-usa.com/product/cz-southpaw-sterling/
I thought Barettas could be shimmed to support Cast On?
I shoot lefty as well but was made too since dad recognized as a kid I had an eye dominance issue same as he did. Its all I know even though I do lots of things right handed. I have never even tried to shoot righty. I would be having same issues as you learning to go right as you are shooting left now. Stay with it and keep focusing on moving gun with your waist instead of arms and it will come to you. It can be done.
A good friend of dads was an avid hunter that lost his right eye to cancer. He learned to shoot left handed and hunted with him for years with my dad. It was only time I can remember seeing three left handed shooters all hunting at same time. He had a glass eye but still wore glasses. I did not know he even had a glass eye for years until he told us. He was a go getter and figured it out. He did not let anything slow him down. He helped my dad build a barn and he was walking around on those loose trusses 20 feet off the ground with no harness like a circus performer. Remember asking him how he learned to shoot left and he said it took awhile but he had to focus on torso muscles and foot work to keep gun moving. He also had to really mentally prepare before each shot. He said after he got it worked out he shot better as lefty than he ever did as a righty.