When you ask about the 2011 I take it you are talking about the STI double stack gun with composit grip.
I don't recall STI having an aluminum frame for the double stack gun but they may have.
I also don't believe they are doing any frames in stainless, I know they quit offering stainless slides several years back.
As for the work required, you will have to change the new frame to the composit grip and may have to fit the frame rails to the slide.
I would also check the barrel timing with the new frame, as it may need adjusted.
Best Regards
Bob Hunter
www.huntercustoms.com