OK, it seems the other car I posted a picture of is a Hispano Argentina "sedán 4 Cilindros".
The Georgano encyclopedia mentions a make of "Motor Criollo" (1938) and says it was started by a Carlos Ballester Molina. Some Spanish-language pages where I see the Hispano Argentina cars pictured mention this guy's name and use the phrase "Motor Criollo," but they don't seem to apply that name to the cars like I thought they did. I wonder if the encyclopedia got something mixed up, and gave a make name that wasn't really a make name.