I don't know what the original gov't specifications were, but it should be relatively easy for manufacturers to find out and manufacture repro. jackets to within those specs and tolerances. Then, unless you are getting a custom tailored jacket, you just pick the size that fits you closest. Most everyone will fit in a 38,40,42,44 or 46 and usually those are the only choices. PERIOD. Just like WWII. Everyone's body is different. Some will fit trim, some will be loose. Some will be between sizes and will have to go one size up. Not many will be a perfect tailored fit. Remember, these were working jackets. So stop fussing you bloody poofters!