Then I got all my pattern pieces from the jacket pattern and laid them out on my pattern paper (aka butcher paper) and adjusted where I wanted to add.
Voila! New pattern pieces!I cut it out of nappy scrappy fabric that I don't know what else to do with and the back worked fine, but the front lapel shape was way off, so I re-measured, drew and cut a new front pattern piece, took the old front pieces off my mock up and put the new ones on. It's closer. The final jacket will have seam allowances taken off all the edges because it will be lined and will also have a collar and capes and sleeves, but no more time to work on it yet, so here's what I ended up with at the end of the sewing session:
A vest with lapels.
I might mess with the lapel shape again--it's not bad though, especially since it will be a bit smaller due to the lining being stitched to it. I also can't change it too drastically because I'm secretly going to put a button loop on one side and a button under my collar so I can close the neck area when it gets real cold so the lapel shape has to be functional (not exactly period correct--they just stuffed the open neck with frou frou, but I'd rather be warm than fashionable). Then on to the mock up sleeves.