"Bridging the South Atlantic" the anniversary envelope states, with a profile of Christ the Redeemer atop its verdant Carioca hill, and the two continents outlined in white. The route line shown is surely wrong, however: antipodean flight paths bend toward the South Pole, not the North.
Few specifications about the flight are provided, as this is not marking an inaugural service (or, for that matter, even a round-number anniversary). The cancellation stamp suggests that a widebody twinjet was employed-- the A300 was the only such aircraft in the SAA/SAL fleet in 1990.
Today, SAA still serves Brazil, but now breezes past Rio to land at Sao Paulo.