How is your other shoulder? I ask because shooting from your "weak" side with a rifle may the the best answer.
Obviously I can't speak to the specifics of your bad shoulder but the 460 Magnum have a widespread reputation for a rather sharp recoil. I suspect that a good portion of those recoil forces will be transferred to your shoulder. In addition to the recoil you'll also have to factor in the effect of holding a handgun this heavy on target, that may place an undue amount of strain on your shoulder. At the very least I would advise you to rent a 460 Magnum before making any decision to purchase, not doing this could end up being a rather expensive "lesson".
As for learning to shoot from your off side, I can tell you that it's actually far easier than you may think. Once you make up your mind to learn how no matter what, you'll find that it only takes a couple of range sessions to become rather good.
As for a light weight rifle, I just happened to pick up a Ruger Scout rifle in 308 Winchester. Weight with an empty mag is 7 lbs. 2 ounces on my scale, so it's fairly light weight. However, I do believe that the 308 may deliver too much of a thump for someone with an injured shoulder, so you won't want to try shooting it on your bad side. Good news is that Ruger builds this rifle in both left and right hand versions. BTW, the recoil isn't that bad for someone shooting from a healthy shoulder as long as you keep it snug. IMO it would take somewhere between 40-60 rounds fired before an experienced shooter started flinching and probably around 100 to cause actual pain the following day. Basically, with good technique it's just a thump and nothing more. If the Ruger sounds interesting Hickok45 has 2 videos featuring this rifle posted on youtube, just search for "Ruger Gunsite". Note, IMO it's a great package and superb value, hopefully Ruger will do a version in 223 for those who like shooting 22's.
