Some 1919 and 1921 race results here: https://acu.com.uy/historia/
I can also offer:
July 19th 1942: Autodromo Nacional. Two known local entries: Eitel Cantoni (Ford) and Jorge Montero (Bugatti-Mercury). There may have been more, but my only source was an Argentinian newspaper! Four Argentinian entries: Pablo Pesatti (Alfa Romeo), Ernesto Nanni (Ford), Mario Chiozza (Mercury) and Rodolfo Martini (Ford). Four more Argentinians were DNAs: Eric Forrest Greene (Maserati 6CM), Roque Brisco (Delahaye), Roberto Firpo (Ford) and José María Solá (Alfa Romeo).
The plan was probably to run two heats for Mecánica Nacional and Coches Especiales and a final, but Pesatti was the only Coches Especiales entrant to arrive, so seems to have had a walkover - I don't think he was required to run it on his own.
MN heat (25 laps, 35km)
1 Chiozza
2 Martini
3 Nanni
4 Cantoni
Final (33 laps, 46.2km)
1 Pesatti
2 Nanni
3 Chiozza
4 Martini
I sent this track map to Darren Galpin some years ago - found it on eBay, IIRC! Can't link the picture, as Darren's site isn't https.
http://www.silhouet....ks/colonia.html