I've decided to make muslins from the bodices of New Look 6401 and Simplicity separately before I try to redesign them into one bodice and the New Look skirt at knee length.
In the spirit of taking it slow, I only cut out the bodice pieces last night.
As advised in Bridal Couture, I made the seam allowances wider by adding an extra an extra 5/8" all around (because I have a 5/8" seam pencil thingie), which adds up to a 1 ¼ inch seam allowance.
I'm concerned that this large allowance would make it harder to sew the princess seams, but I'll worry about that when I get to that stage.
I also had a hard time aligning the fabric grain, and gave up when I couldn't align that last quarter inch hanging off the edge of the horizontal grain. After cutting the muslin fabric, I decided that was enough work for one night and I made another drawstring bag as a satisfying way of ending my sewing session.
I plan to trace the markings tonight, prepare the skirt pattern and make another drawstring bag. I think working slowly and methodically on the dress while making little projects on side will keep me from going crazy over the dress.