The assimalados had equal rights
Ah yes, the assimilados, AKA like 2% of mixed race, and only 0.8% (IIRC) of the african population.
Also the requirement to become one was stupidly high IIRC. As always the answer for a better 20th century for portugal always has to come to education, education, education, make reforms in the 30s
I really see no more grounds for a partition of Portuguese Angola than I do for a partition of French Algeria. In both cases, the populations of the colonized and the colonizers are too intermixed for anything short of a brutal partition with massive population exchanges to create a division.
Intermixed? If you mean a mixed population, it was as i said very low, and most in cities, as for the white population was overwhelmingly Urban (mostly coastal cities+ Huambo/Nova Lisboa), outside it was either plantation owner, small traders or soldiers, the countryside white farmer population was very low (a few thousand), and the countryside settlement effort in the 60s failed spectacularly (the whites often had worse output than the native they took land from, and there are even accounts of MPLA insurgent taking pity of them and deciding not to attack them).
Any "partition" of angola that aims to limit settler movement would have to include all the coast and would result in a large african majority, a north-western state would need the movement of over a hundred thousand white settlers.
Mozambique's settler population was much more focused in the south (beside it only beira had a large population), a state entirely south of the save river could very well work demographically, especially if angolans settlers are moved there. Only problem is that it would be at the mercy of south africa economically and politically and portugal would always be seen as an ally of apartheid (and if they try to oppose South Africa, the latter will just cut most trade and will make that southern mozambican state's economy collapse)
Also, I don't see why integrating 3 million blacks would be a problem.
In the immediate it won't, but inequalities will stay, in the long run (after a decade or two) you're going to have a Northern Irish/New Caledonian problem on steroid. Expect a second insurgency in the 80s/90s that will cause thousands of additional death. I'm not even talking about immigration from neighbouring countries which will be a huge problem (although it could potentially be an issue both independantist and loyalist sides would agree with).
Ideally you'd want to maybe send a million or so of native angolans to the portuguese mainland, where they would hopefully assimilate, and at the same time open the gate to brazilian immigration (2 million brazilian left, mostly to the US, in the 80s-2000s, only 150-200k went to Portugal IRL, that number can be boosted especially if luanda is a quickly developping city.