There is an interior photo on page 131 of my hard copy of the USAF pub "Search and Rescue in Southeast Asia". The book is available in PDF format off of the USAF history publications website at https://www.airforcehistory.hq.af.mil/Publications/titleindex.htm but I don't know how well the photos show up. Very similar to the photo you posted from the airliners website, has a few floor details visible and other details that can be made out.
In addition, the Squadron in Action pub on the H-3 Seaking also contains a section on the Air Force HH/CH-3s. No interior photos, but some nice drawings of the gun mounts for the window and ramp.
I have the old Revell kit in the stash for a future build. Just wish someone would give us a modern 1/72 or 1/48 scale kit of an HH-3!