Angola–Democratic Republic of the Congo border
The Angola–Democratic Republic of the Congo border is 2,646 km (1,644 m) in length and consists of two non-contiguous sections: a 225 km (140 m) section along the border with Angola's province of Cabinda, running from the Atlantic Ocean to the tripoint with the Republic of Congo, and a much longer 2,421 km (1,504 m) section running from the Atlantic to the tripoint with Zambia.
Northern (Cabinda) section border crossing
The border starts in the west on the Atlantic coast, proceeding to the north-east by an irregular and then a straight line, before turning to the north where it then proceeds in a straight line up to Luali river. The border then follows this river north to the confluence with the Chiloango, then following the latter as it flows to the north-east up the tripoint with the Republic of Congo.
Southern section border crossing
The border starts in the west on the Atlantic Coast at the estuary of the Congo River, following this river eastwards for a period before leaving it just north of the Angolan town of Noqui. It then proceeds in a roughly straight line eastwards, occasionally utilising rivers such as the Mpozo, Lufo and Luvemba, before reaching the Lubishi river, following this briefly to its confluence with the Kwango. It then follows the Kwango as it flows to the south, before turning east at the confluence with the Utunguila. The border then proceed eastwards, utilising a number of rivers (notably the Lola, Wamba, Kombo, Lucaia, Kwenge, Luita, Congolo, Lovua and the Chicapa) and straight overland lines (including the 7th parallel south and 8th parallel south), before reaching the Kasai River. The border then follows this river, and then the Luao, as they flow to the south, before turning east and proceeding overland via various irregular lines to the Zambian tripoint.
Democratic Republic of the Congo – Angola border crossing
This part of Africa on the Atlantic coast is quite tricky: between the southern parallels 5° and 6°, from Pointe-Noire (Congo) to Soyo (Angola), there are three border crossings within less than 200 kilometers. And those are not easy countries to get in: the Democratic Republic of Congo (DRC, ex Zaire) and Angola.
Fly from Matadi to Boma then on to Muanda on the coast. From there you can easily take a taxi north into Cabinda City. Technically that puts you in Angola, and all you need is an internal flight south to Luanda. These flights run all day and were around $120
Crossing by Bus
A bus was supposed to get me from Luanda to Santa Clara at the border with Namibia. It's a 1,000 km trip but the roads are fairly good and the busses are comfortable so it should have been okay.
Crossing broder Angola from Kinshasa by land with local transport?
You will not be allowed to cross into the DRC there with an e-visa, as they only email you a PDF approval document. You then present that printed PDF at the border to be given a whole-page visa sticker, for which they need to take your photo and print it. No way they'll be able to do that up by the Matadi border posts. Nor will they be willing to, as your approval "Carta de Autorização de Visto Turismo / Negócio" specifically states which border you will collect the sticker from