I bought a nice new 118 perfecto in NYC shop around 1991. It seems to be a 44 size as displayed on (main and) hidden labels: 2949 / 031 / 118 / 44.
It fits OK.
I tried recently to look for an another perfecto 115J (on schott web page https://www.schott-store.com) and I tried to compute my regular size using the following parameters:
H 5' 9" W 159Lbs Chest 39/40 The output was 40.
How do you explain the difference, which size I must choose for a 1991 perfecto and for a 2020 perfecto?
The outside dimension at chest (inside the upper of sleeves) of my 118 (size 44) is 23" and at the top between shoulder board extremities is 20".