According to Wikipedia the entire SADF was circa 80,000 by the late '70s. Not sure what it was in the '80s. Presumably most of this was the army:
http://en.wikipedia.org/wiki/South_African_Army#The_.22Border_War.22_.281966.E2.80.931989.29
That's much larger than the 12,000 Argentine troops in the Falklands. And the SADF had something like 130 MBT's.