In the 70's, Shinjin cars in Korea began a relationship with General Motors, changing the brand of most of its vehicles to Chevrolet, or GM. The first basic looking pickup is called a "Saemaul" truck. Interesting!! Via lifelog.blog.naver.com/.
|GM Korea Saemaul truck 1974-09-23|
The other trucks look like Isuzu, certainly the first is one.
|Chevrolet truck 8 T 1974-04-15 GM Korea|
|Chevrolet Korea 6.5 tons 8 tons 1973-05-18|
They also remind me of this picture of a Chevrolet badged Isuzu Elf, from a 1977 Saemaul book (more scans here).