Here is a Shirt/Tunic construction guide from the 1930's.
I have brought this over from the Cutter and Tailor Forum.
It goes with the Parson's Tunic draft:
http://movsd.com/BespokeCutter/index.php?topic=1009.0
(https://i.postimg.cc/YLY3K7hw/Herbert-Parsons-Tunic-Construction.png) (https://postimg.cc/YLY3K7hw)
(https://i.postimg.cc/rzGTNrwQ/Shirtmaking2.jpg) (https://postimg.cc/rzGTNrwQ)
(https://i.postimg.cc/n9p6P3hT/Shirtmaking3.jpg) (https://postimg.cc/n9p6P3hT)