Thanks for quick response.
First, a correction: the large raw clip was the 16-minute file, not the full, 40 minute file.
Still, iMovie wouldn’t allow the entire 40 minutes of raw to be imported (yes, plenty of room on the external drive).
Since I only needed a few clips from the entire raw, I just found each in- and out-time & imported them separately with no issues.
I can edit with Quicktime? Split clips, adjust audio levels?