As I understand it, the Portuguese were still only in control of the coastal areas of Angola and Mozambique in the 19th century, but claimed a stretch of land connecting the two which they didn't have the cash, population or inclination to occupy. Then, in 1889, John Cecil Rhodes raced Leopold II's Stairs Expedition to establish colonial rule over the native kingdoms in modern Zimbabwe, Zambia and Katanga and basically won. The Portuguese were a bit miffed and asked their oldest allies to stop cockblocking them, but the British told them where to shove it and King Carlos ended up with a bullet in the head.
So how can Lisbon reasonably either properly colonise the interior before the UK gets involved or convince Britain to allow them to retain their claim in return for (presumably) letting the British South African Company trade in their lands and build that bloody Railway if it means that much to them?
Additionally, how does this affect Britain, Portugal and the colonies themselves? I'm assuming the East-West axis will mean better cross-continental lines of communication which will be a boon come decolonisation, for a start.