Has anyone seen a ported DR pre-WWII like this one that Kirby has listed?

https://www.vintagedoubles.com/catalog/?sort=5

Gun ID: 4851

[Linked Image from thumbs2.imgbox.com]

What kind of knock does it take for the addition.

Too, I can't put my finger on it, but the front sight has multiple functions or similar.

Serbus,

Raimey
rse