In the mid 80s, the Thomson Holidays series to Yugoslavia (from Luton anyway) were operated by Inex-Adria (as it was then) using a mix of DC9-30s, Dc9-50 and MD80s. I flew to Pula in 1986, out on DC9-30 and back on a DC9-50.
Yugotours holidays at the time were operated by Aviogenex, using mainly B737s. Prior to the 737s one got to go on a TU134!