I did a "southpaw Stenling" once just because I am left-handed and a self-indulgent idiot. Of course the parent gun wasn't worth anywhere near what it would be worth today. It couldn't be a true mirror image because the cocking handle slot couldn't be moved but having it on the right side actually works well for lefties anyway.
Moving the mag catch from the top of the magwell to the bottom (since it was rotated 180 degrees) wasn't too bad, but the bolt had to have the cocking handle hole carefully relocated and a custom wider cocking handle (to accommodate the wider Sten slot) had to be fabricated. The rest was pretty easy. The selector switch can be reversed, the barrel needed a clearance slot for the extractor cut on the opposite side of the original one and some sheet metal needed to be moved to make the swap between the ejection port and the attachment area for the magwell. Scott Andrey made me a custom barrel that was extended and threaded so I can screw a can on it and I got rid of the bayonet lug because it was in the way of my fingers and bayonets on subguns are stupid anyway. Obviously, a Sterling purist would puke all over it but I enjoyed the project and it's very nice to shoot left-handed. Oh, yeah- the magazines just need a small milled cut on the side opposite the original "shelf" that the mag catch uses. They are still fully functional for a normal Sterling. Just to make it worse, I modified a 50-round Lanchester mag also, just to have one.
It's fun walking up to the firing line to the right of one of your buddies and showering them with hot brass from an unexpected direction! Revenge of the lefties!