A Macoco Alzaga Unzue Mercer?

PS. The 1919 raceabout model was identical to the 1917 and 1918 model by the way, so the earliest moment to purchase it would have been the fall of 1916.

No doubt about Mercer, as Robbie Marenzi already stated. I must admit that I ruled out Mercer at first because of the louvres, but a simple check confirmed his comment. However I guess it's a 1919 model, which didn't seem to have had a standard wind screen. Besides there were some other small differences such as the more pointed top of the hood. The 1919 model matches perfectly (except for the fenders and missing running board of course). I uploaded images of the 1919 and 1920 models, so you can compare yourself. See here: http://www.prewarcar.com/prewar-my-prewarcar/spot-a-pre-war-car/argentinian-mercer-mystery-026213.html

Could be a 1914 Mercer.See that Macoco was too young and he often used to buy used cars.

My guess would be Mercer [not Stutz]. I recall a pair of those rather distinctive fuel caps being offered for sale on PWC. Also the radiator is the shape of a Mercer and the image that you posted of a Mercer is virtually identical. Of further interest is the image of the man himself on the link you post. The car he is sitting in looks very French to me [steering wheel/oil pressure indicator]. How great it would have been to be a wealthy person in this period and be in a position to purchase such cars.

Stutz Bearcat 1918?

I think there's no doubt it's a Mercer Raceabout, most likely a 1920/22 Series 5, L head, still no front brakes, but with 32 x 4 1/2 tyres, smaller than the previous model 22/73. Five louvers on the bonnet, the 22/72 had only three, bullet shaped headlamps, Series 6 had drum shaped lamps. Seems very much standard except for the missing windscreen, running boards and the racy mudguards. The petrol level gauge can be seen on side of the tank.
There’s no way of knowing where the picture was taken, but it looks like a former stable/coach house in a city, it could easily be Buenos Aires.