This is the fellow who supposedly was sucked out of the "DC-8"...
...I understand he survived a whole string of accidents and then wound up winning a shedload of money on the lottery.
However, I digress. I suspect that if he was flying between Zagreb and Rijeka then it was with JAT. I don't recollect JAT having DC-8s, and no DC-9s until the 1970s.
Perhaps a DC-6?