JAT initially bought the 707s for their long-haul services to the USA etc. They never bought a new one, but started off with former Pan Am turbojet-powered 707-320s, then moved on to fan-powered ones as they came onto the market. In 1978-9 they started on a DC-10 fleet for these mainstream flights and the 707s, probably pretty much at residual value by then, got used on a range of charters, to various UK/German/Scandinavian points, and were also leased out off-season a bit longer term. They turned up on the Hadj from time to time, of course.
Yugotours were a UK tour operator but owned behind the scenes from Yugoslavia. Most years they only used Yugoslavian airlines, from a wide range of UK points to a mix of Dalmatian coast points. They were notable that they only appeared to operate UK flights on Saturday/Sunday, and no night flights, which must have given them a significant advantage in the holiday market, so presumably their chartered aircraft didn't rack up many hours, and the 707s fuel burn wasn't that important in overall costings. I recall seeing three Aviogenex Tu134s lined up abreast at Manchester on August Saturday mornings. That was probably an even less economical aircraft per passenger seat than the 707. Their pilots were a contrast to the rest of those down on the ramp, especially 30 years ago, in not wearing ties !
Apparently 707 YU-AGJ, one of the JAT ex-Northwest 707 pair, which was sold onwards in Africa, still languishes in the weeds at Kinshasa. Possibly one of these
https://www.google.co.uk/maps/@-4.38.../data=!3m1!1e3