Long story short, I took a pattern from the Winter 1952/1953 issue of McCall’s Needlework and changed the gauge, size, and style (from a box coat to a swing coat). Twenty balls of sport weight yarn and one month (exactly!) later, I ended up with a perfectly fitting coat. (OK, the sleeves could stand to be a bit wider, but I have one foot of yarn let, so that’s not going to happen.)
Good Man was incredibly helpful, because he wore it while I tacked down the double-petal collar. In turn, he sort of ended up looking like some communist student from the 60s.