You can get the sling swivel you pointed out, but I find they hold the barrel too low, so that causes the rifle to flip over when you carry it slung in front of your chest. Care of the US Army, I carried a rifle many, many hours. GG&G makes a sling mount that gives you a quick detach mount and it bolts through the hole in the front sight base. So the weight of the barrel is below the sling and the rifle sits properly. In actual day after day use, you carry a rifle hundreds of hours for every hour when you take the rifle in a low ready or similar imminent posture.
As far as a sling throwing off the point of aim, yes it does if you are tightly slung up. But if you are carrying a rifle for days on end, and you need to use it, you just don't sling up when you fire. It's not a competition and you are not likely to be engaging a target hundreds of yards away. Note that I do shoot more accurately at range with a sling, but in a "carry" environment I think it is lower on the priority list than the rifle "laying" in a comfortable and convenient position.