This relates back to the Pelikan entry of a few days ago. As suggested, I contacted Rick Propas and he very kindly replied almost immediately. Here’s what he had to say:
Always hard to tell just from images, but it looks to me like an M250.
Put it up against your M400 should be the same size, if not it could be
an M150 fitted with a gold nib. Regardless, nice piece.
Taking size into account, it looks like it’s an M250.
Goodwriterspens's Blog 
Hi, I’m a new reader to this fine blog. FWIW, I think this Pelikan could be an M481. Find more here:
https://www.pelikan-collectibles.com/en/Pelikan/Models/Classic-Series/M200-Basis/index.html
and
https://www.pelikan-collectibles.com/en/Pelikan/Models/Classic-Series/M100-Basis/index.html
You can tell it from the absence (or not) of the Pelikan logo on the cap top. I happen to have one of these. The presentation box is not as gorgeous as yours, and bears a label which says “M 150”. But I have also an M 150 Old Style, which is smaller, whose cap ring is beveled and which sports the logo on the cap. Somewhere in the transition Pelikan probably dubbed this pen as M 150.
The pen is the very same size as a modern M 200. The caps interchange, the only difference being in the cap top. The nib of the M150 is also interchangeable but it’s smaller.
A seller told me they were run in small series with a gold nib, 12 carat, (with the engraved lines not meeting at the nib slit), probably as corporate gifts or like.
My pen had actually been a corporate gift, that a friend passed to me. The nib is a HEF (Hard Extra Fine) which needed a bit of tuning to be made to write Pelikan style.
All the best
Dria
Savona, Italy
Thank you, Dria, for all that informtion. Pelikans can be very confusing! Vey kind of you to make the effort.