Got the mock-up done! Fitting has always been stressful for me, but I think this one went okay.
My base pattern was Laughing Moon's Early 1860's Day Dress. The bodice portion with coat sleeves.
|via Laughing Moon|
I made the armscyes bigger (they were digging in under my arms), narrowed the sleeves, widened the neck, and took in the waist about a 1/2 inch. I also lengthened the bottom edges a little. I decided that I may want to extend the bodice into the little skirt thing. If I leave a little extra room at the bottom, I will have the proper seam allowance to add that piece below the waist. Hmm... Maybe this shows what I'm trying to say:
This is Queen Victoria's riding habit. (Looks a lot like what I'm going for!) See the part where it flares out from the waist? That's what I might aim for. On the men's tunics, it's a separate piece sewn to the waist. Dunno what it's called...