You can find tutorial for finishing off the arm hole so that the pattern becomes a vest.
https://www.amazon.com/McCalls-Pattern-Misses-Jacket-Costume/dp/B071WM9MCG/ref=asc_df_B071WM9MCG/?tag=hyprod-20&linkCode=df0&hvadid=216539702338&hvpos=&hvnetw=g&hvrand=8056586416702382008&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9003439&hvtargid=pla-350804746745&psc=1
http://westernpatterns.com/shadbellycoat.aspx?ref=equinewebdesign
Search terms "Shadbelly coat" or "double breasted vest with coat tails"