[nuyt]

According to Hugh Thomas (The Spanish Civil War) the Ford and GM works were seized in Barcelona, in early August 1936. After a protest by the American government, the Spanish (=Republican) government undertook compensation. But "government" was a fluid notion. The Ford works came under control of the CNT forces (page 295). There's no mention of who took over the GM, but most likely it was this force as well.

Paul Preston (Franco biographer) names military aid by the US as: "military equipment confined largely to equipment surplus to the general NATO build-up, weapons, aircraft and vehicles already used in WW2 and/or Korea (p 623).
In exchange there would be US bases at Torrejon and Rota (still there anno 2004).
Second rate stuff. But soon ther would be Chaffee tanks, halftracks, M8 armoured cars, C15TA and Walker Bulldog tanks! (Nuyt)

I am not sure if there was any military cooperation between Spain and Portugal around 1940. Franco dreamt of taking over Portugal, though some sort of friendship treaty was signed.

Most logical origin of the GM and Chevrolet 1940 trucks would be civilian imports to Barcelona or through any other factory, like Lisbon (but we also know DAF provided Spain with Trado converted trucks during the Civil War).

To take the subject somewhat further: In a book called Les Chasseurs d 'Afrique by Sicard and Vauvilier there is the following entry on page 129(There is obviously some legend that the French army took over a number of GMC 4x4 trucks (ACK353) from the fleeing Republican forces in 1939. True or not, we shall find out):