You looked up a five digit number, not six. Your machine is a 128. Yours was made in 1937, mine is a 1952. A 99 doesn't have the shuttle instead of a bobbin. You can find a manual at ISMACS of sew-classic.com I downloaded a copy of the original from sew-classic. The manual includes a treadle, which I think is the 127.
Singer 128 with the blackside finish
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