Thanks for the nice comments on Marfy 2608.
Here is the second fancy dress I've made in the past month. Don't tell the others, but this is my favorite! I had a vision in my head, and against all odds, the finished product is exactly what I had hoped for! I was able to find the lace I wanted and a suitable pattern to make it happen.
I showed some of my construction process, including the lace muslin, here. The pattern I used is Vogue 7852, so out of print, it's not even on the website anymore. The entire strapless underdress was made exactly from the pattern. The lace shell is cobbled together from pieces of that pattern to make a darted sheath.
The zipper is the only place where the lace shell and the strapless dress are connected. I treated the lace shell and the outer layer of the strapless dress as one to put in the invisible zipper. Then, I hand stitched the lining, including the foundation, to the zipper. I think it's a nice clean finish inside. I constructed the foundation on the lining, after using a lightweight, woven interfacing in the boned portions. The outer layer of the strapless dress has a cotton flannel underlining on the boned portion, to pad and camouflage the boning from the outside.