I was trying to figure out what year my .375 was was made. I dont know the serial number off hand, but it does not have a barrel band swivel, it is in the forearm.

should be a date on the receiver at the woodline....

if not, it WILL be marked on the barre

Should be a 4-digit number on the right side of the rear bridge. Supposedly the last two number are the year of manufacture. I am only reporting what others have said, such as here
here.

Here is the rear bridge, right side, of my .458:

Colin ; Interarms also had the Alaskan model in 458 Winchester. It had Williams open rear sight . No barrel band sling swivel post . And a Monte Carlo stock . The Whitworth Express had the classic African style stock with shadow line cheek rest. Wide shallow V express sights and barrel band sling swivel post. .
Anyway, just my 2¢

I have a .375 that in reading the descriptions posted so far, is possibly a bastardization of the Whitworth and the Mark X Interarms rifles.

According to the information listed in one of the earlier posts, it appears my rifle was built in 1975.

On the left side of the action it is stamped with the Interarms Mark X logo.

The odd parts if I am reading the information that has been posted correctly, one of the anomalies on my gun is that it does have the front barrel band, it also has a black decelerator butt pad and it appears, the African style stock. I was under the impression that the Whitworth Express were marked with that logo. anyone know for sure?