About the Portuguese Navy holster.
In All period photos I could find they were wearing M2 type holsters. But the truth is all those photos were of "landing parties". So I suspect they were are armed with M2 pistols. One has to remember the original Navy contract was for only about 500 pistols(and it got divided almost in half because of the Republican revolution of 1910.
About half of them have the Crown over Anchor and the remainer have R. P. over Anchor). Cannot find a photo of a ship officer carrying a pistol.
IE.
However, There is this photo(These items belong to an ex forum member) of a Navy Pistol complete with holster, that apparently was owned by an Admiral.
Edit. Looking closer at the first pictures. I'm not so sure those are M2 holsters.