Other adjustments are challenging because of the way princess seam dresses are constructed. On most of them, the shoulder straps are part of the bodice front. Thus I couldn't alter the bodice front to accommodate my narrow upper chest without skewing the shoulder straps and armholes.
I finally found the solution in McCall's 6027.
In this pattern, the shoulder straps are part of the bodice side front, leaving me free to alter the bodice front without skewing the shoulder straps.
Even better, the bodice front has a seam down the center, giving me an easy reference for narrowing the bodice.
After making a muslin and using myself as a human
The photos below show a comparison of the original front pattern piece and my front pattern piece. Luckily, I did not have to change the curve of the bust seam, which meant I didn't have to alter the side front pattern piece. I was able to get the proper fit by making changes only along the center seam.
There is one big drawback to McCall's 6027 -- it's too low-cut for me. The easy solution is to wear it as a jumper (a sleeveless dress worn over a shirt). It's very comfortable, but I suspect it makes me look like a schoolteacher.
This is especially true in the Halloween fabric I used for my first successful prototype.
I have since made three more jumpers, with some variations, which I will show in upcoming posts.