Step 26 of 1.B.3 has two issues.
- The caption and the screenshot give different values to supply to Part Lightening:
- Regardless as to what values are used, v54 of the Part Lightening feature script doesn't generate pockets. It errors out with "Failed to shell and offset bodies". A much smaller diameter tool (this varies depending on rib size, but .05 works for both sets of values) allows the feature to generate. The top left hole of the motor mounting appears to be the issue. Removal fixes the problem:

Step 26 of 1.B.3 has two issues.