...so people like janitors and accountants were classified as "manufacturing" workers simply because they worked for manufacturing companies....
Non-productive workers were included in your skewed numbers, Not to mention the government dictated what they'd pay for the material and equipment contributing to the skewed GDP numbers.
Taking that into consideration I'd say their productivity was better....
I'd like to see an American ship builder (are there any left?) match the production of Liberty ships today like Kaiser did then.