Also from the link I posted
above (terrific source for all bass things Gibson):
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"All models have a
rosewood fingerboard, dot inlays,
maple neck and transfer instead of inlaid logo.
Body wood is most likely alder (although this was never specified for the 300/400). This is the first Gibson bass with a maple neck (the EB series went maple-necked in '72), and the first sold-body not made of mahogany." (Emphasis mine.)
In the publicity sheet
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body wood info is indeed glaringly omitted - Gibson must have decided to leave it undisclosed for some reason:
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