Looking at pleating diagrams from the previously mentioned books is very helpful as you're doing this next step!
Pin the center back of the pleats to the center back of the bodice. I found this easier to do off the form than on it.
Make a narrow inverted box pleat in the center. Mine is about three-quarters of an inch deep. If you notice, the fabric is already setting itself up for the next pleat!
Make the outer pleat. This should be wider at the top than the bottom. Just futz with it--there's no science to it. The size and shape of this pleat did change over the century, so it's best to look at extant dresses to see how you should shape yours. Just be sure to not make this smooth, as the next pleat sits on top of it!
Make the next pleat. This should sit on top of the first, and allow a little of the first to peek through.
Repeat on the other side! They don't need to be perfect. As long as they're visually similar, you're fine.
Now, pin the front pieces on. You don't need to match the seamlines. I wanted a slightly smaller look to the back, so I cut my front pieces a little longer. Match the front around the bottom of the armscye, fold the seam allowance under, and pin into place.
You'll notice there's a little leftover at the bottom. Tuck this underneath the back bodice as shown. This will allow you to turn up the bodice edge all the way around the front of the skirt.
Repeat on the other side. Then, using a spaced backstich, sew! I started at the sides and then sewed the center back. Be sure to smooth things out each time you sew--sewing does shift things a little. Trim the neckline edge.
And with that, the back of the dress--well, except for binding the neckline--is done!
As I write this, I've also sewn the sleeves, stomacher, and front skirt pieces to the back. The tutorial will continue soon with the front of the dress!