This video covers the removal and replacement of the screw type stitch length regulator commonly found on vintage Singer sewing machines such as the 127, 128, and early models of the 15, 66, and 99.
EDIT: I just added a video specifically addressing the Model 99 and the lack of a hole in the back of the pillar. You can find it here:
https://www.youtube.com/watch?v=6fpVqk_7lBI
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