3rd August 1909: birth of Denis Carey, who played Professor Chronotis in Shada (unbroadcast but would have been 1980), the Keeper in The Keeper of Traken (1981), and the Old Man (the front identity for the Borad) in Timelash (1985).
3rd August 2002: death of Carmen Silvera, who played several parts in The Celestial Toymaker (1966) and also Ruth in Invasion of the Dinosaurs (1974), better known in later years as René Artois's long-suffering wife Edith in 'Allo! 'Allo!.
ii) production anniversary
3rd August 1989: I don't usually do anniversaries of the often tediously well-documented process of making Who, but this one is special: the final day of filming of Ghost Light, the last scene ever made of Old Who being the one where Gwendoline and her mother are turned to stone. And that, as it turned out, was the end, save the final voiceover for the last episode of Survival.
iii) date specified in-universe
3 August 1975: Setting of chapter 3 of Oli Smith's 2010 Eleventh Doctor novel Nuclear Time. (Most of the rest is set on 28 August 1981.)