I continued working on Round 1 of alterations on Butterick 4915 this evening. I now have two altered pattern pieces, the Upper Front and Upper Back. I'll be using them along with the unaltered Middle Front and Middle Back pieces to construct a bodice muslin for a fitting on Thursday evening. Pictures will be forthcoming.
Thanks to Marita and Birgitte for your advice, and to Gwen for stopping by and offering some moral support. I really appreciate you taking the time to help me out or just to let me know you're there.