We're also going to be heading north later this year. We've spoken on the telephone to the Angolan consulates in Namibia, in Windhoek and also in Oshakati near the Angolan border. Both told us that they will only issue visas, whether tourist or transit, to residents of Namibia (and probably, I'm not sure, also residents of other countries in the South Africa Customs Union). We're from the UK, so that's not much help.
Maybe they are more helpful when you see them. Has anyone any experience of getting an Angolan visa, either tourist or transit, in Namibia or Botswana?