(Please excuse my ignorance.) In the shuttle, on the wafer, are all the dies the same, or are they different across the wafer and replicated using multiple wafers? (Is the shuttle using multiple wafers?)

I don't know specific details for this tapeout but for the ones I have worked on in the past, the masks were for a roughly 25mm x 25mm square region of wafer, I think caled the "reticle" and that reticle was repeated in a pattern all over the wafer. There would be several wafers in a batch, perhaps 25 or so, all wafers typically being identical. You could put as many designs as you can fit inside the reticle. Typically all of the sawcuts will be straight and will go right across the wafer, so as FatsieFS points out, if you don't want to ruin any chips then they all should be the same size.