Reinstallation is in progress.
Before the reinstall, I could at least do a flight without the Duckworld mod, just for a quick check.
After I removed the mod, there were no more missing textures (and no more avatars unfortunately) and I could take a closer look.
This time, the cockpit scale looked much better indeed.
To clarify before I go further, the Duckworld mod is nowhere faulty. It's just that I had made my experiments to add the avatars (amongst other things) by altering the files in the Duckworld mod folder, causing it to be faulty so to say. I had also tried to modify some files in the "official" folder, but this was a total failure so I went on with modifying the files in the Duckworld mod folder instead.
The brief (before I deleted the mod) appearance of the avatars in the cockpit was an quite eye opener though. It was a confirmation that the cockpit was indeed in the correct scale
After thinking about it for a while, I realised the problem I describe, about the lack of space for the legs/knees between the seat surface and the yoke body, is probably a consequence of the fact that the cushion of the seat is not compressed at all by the presence of the avatar... leading the avatar to seat actually a bit too high, which could be an explanation for the seemingly missing space...
I took some time to look at the seat more closely in VR, after positioning my head more appropriately. It still looks a bit small, or more precisely "narrow", but at least now it seem my ass *could* fit in there
So again, I apologize to AH for my previous comments regarding the cockpit scale. It was apparently the result of some bad edits from my side, which are being wiped out as I write this message. The reinstall is taking a bit longer than I hoped, so I won't be able to retest a "clean" DC-3 tonight it seems, but tomorrow should be fine.