I got a 30 day tourist visa in Cape town and it took about a week, or 5 working days. See my post here:
http://www.horizonsunlimited.com/hub...ist-visa-52457

At the embassy there were tonnes of people applying for groups, etc. They'd have a stack of passports with applications and hand them in all together. I think the majority of them were work related visas, but either way, a visa service is certainly an option that people use in Cape Town.

you should be able to get a tourist visa with some effort.
Have a look at the south African 4x4 community site. They have a section on Angola and some trip reports.
apparently the Flamingo Lodge will issue a letter of invitation.

I'm going north through Angola in november/december, and yes - The Flamingo Lodge does issue letters of invitation. I just had it confirmed.

Contact person at Flamingo is Raymond Sakko: ray@aasafaris.com