After my washed, blocked, and dried swatch hung with weights for a day, the gauge measures 27 stitches and 39 rounds = 4".
The gauge for the sweater is listed at 6 sts/inch (page 93 of The Knitter's Handy Book of Top-Down Sweaters). I like the density of my swatch and wouldn't want to change to larger needles (and a looser fabric) to match that in the pattern. Instead, I want to see if I can follow the instructions for a larger size and end up with the size I want.
I'd like a bust circumference of 40", which means I need 40" x 6.75 sts/in = 270 stitches just below the armhole. The total number of body stitches are given on page 96, at the end of the heading "Divide for Body and Sleeves. The largest size has 276 stitches, which would translate to a bust circumference of 40.9" at my gauge. The second-to-largest size has 252 stitches, which would translate to a bust circumference of 37.3". Neither of these is exactly what I want, but the largest size is closest.
I've decided to follow the instructions for the largest size for all stitch counts, but because I'd rather err on the smaller size, I think I'll omit the last raglan increase so that I'll end up with 268 stitches for the body. That will give a bust circumference of 39.7".
I'll count rows rather than simply measure vertical distances to make sure that the lengths will reflect the after-hanging row gauge.
It's time to cast on!