UPDATE: I took one slide and placed it on a 1140 ‘canvas’ with a black background, put it on the site and just as you said, it centers fine.
It was always easy to ‘find’ slides .jpg that are 960×350 out of the box, so to speak… as it is a common size. But 1140×350 isn’t so we are going to have to do more work for this theme.
Maybe we’ll just still with the old Legacy of 960… if I can find a clean copy of it somewhere. Is there on on your site I can download?