Hello
I think it's time to close the challenge ...It seems it's really a rarity!
Aviation Magazine 1951 tell us ,it is the:
MANTELLI AM-11 Albatros
single seater built by the "Club Argentino de Planeatores Albatros" at Buenos-Aires.
When googling AM-11 ,we got another Mantelli aircraft ...
Thank you for participating
Skytrain ,you owe the control
(have you a pic of the PM 12 glider ?)