Okay, so here's the cardigan finished. I added ribbing around the bottom because the single crochet didn't really keep the back from rolling up along the bottom edge.
Here's a photo before the bottom ribbing was added. It's hard to see because I was holding the bottom in place, hence the ribbing decision.
I do very much like this pattern, and I have pulled a gorgeous colorway of Kochoron for another one. This time I will make the next larger size (finished bust 40") This fits well enough, but there's not much ease.
On the next one I'm going to try another edge treatment that is sure to prevent rolling but doesn't require an edging or ribbing.