If you can comfortably pull back a compound set at 53 pounds, that should be more than enough provided your arrows are flying true and your broadheads are shaving sharp. As long as your arrows are flying straight, they should pass right trough the rib cage. I only shoot 60 pounds myself and have never failed to get a complete pass through when shooting trough the heart/lung area.
If you haven't looked at compound bows in a while, you will be very surprised at the speeds even a light bow will throw the arrows.
My advice, FWIW, is to go to a reputable pro shop and explain your limitations. They should be able to set you up nicely.
Good luck, also, now is not too soon to start. You have a lot of time to develope good shooting muscle tone, which will be very important, considering your "bum shoulder."