Could we potentially have Angola remain Portuguese? If I remember correctly, the Portuguese had already been quite successful in driving out rebel groups so could we see Angola remain attached to Lisbon as an Overseas Province?
Maybe, but they would need 1) major economic and military support from other nations, and 2) to let everything else go. Even then it's iffy
By 1974 Portugal had definitely won the war in Angola, was clearly winning in Mozambique and had reached a stalemate in Guinea-Bissau. If we conveniently handwave the Carnation Revolution, Portugal could technically keep its African colonies without ditching anything except perhaps Guinea.
That said, you can't just handwave away the revolution. Popular support for colonialism and the Estado Novo regime was practically non-existant by that time.
You can save the entire Portuguese Empire, but you need a 1940s POD (latest)