That Pederson Device made for the Moisin Nagant rifle was part of a Guns Digest article "The Secret Pistol of World War 1".
The author had all 3 devices, one each for the 03, 1917 and M/N.

He explains the differences between them and the mods done to the rifles to accept them. From what I gathered, the 03 and 17 mags were the same. The M/N a completely different set up and mag inserted from the high left.
No ejection port needed, just a slight relief cut to the receiver wall for the mag to clear.
He test fires the M/N with the device for the article.
I got the idea the 1917 and M/N Pederson Devices he had were one-of designers original patent models.

Interesting article.
1968 Guns Digest, page 220
It has a list of 20 (at the time) known devices and their location(s) & conditions .

I've only ever seen one. At a Syracuse NY gun show in the 1980's. For sale along with a MkI '03 it was displayed in.
I don't remember much about it other than what it was and the crowd around the display was 10 deep most of the time.