I was thinking the same thing. I have a Oberndorf built "Modelo 1907" it's .980" small shank. .100" longer threaded area
But I think his rifle is purpose built commercial rifle. Based off the info I found on my receiver.
"the Oberndorf intermediate action, as they are the only ones who produced it. Commonly encountered models include:
1903 Turk
1909 Peruvian
1935 Argentine
Oberndorf Commercial
The 1903 Turk and the 1909 Peruvian also share some other qualities. They both have a very high clip bridge, and a long curved arm on the ejector box that puts pressure on a stripper clip loaded into the receiver, holding it in place. The 1935 Argentine and the Oberndorf commercial action do not have this.
This type has a longer than normal receiver ring, and a longer than normal cocking piece, with a shorter than normal bolt body, hard to figure where the weight savings come in!
The Oberndorf commercial action was also available in a small ring version, all other dimensions identical.""
This is the same receiver, I built a 43 Express on the action
https://www.canadiangunnutz.com/forum/threads/what-type-of-mauser-receiver-is-this.1905542/