A TL I've thought about but never fleshed out, even mentally, is Francoist Spain getting a little more confrontational with the UK over Gibraltar. To stick a thumb in the eye of the former colonial power (not to mention get access to the petroleum resources), Spain backs Biafra from Spanish Guinea with weapons, air cover, naval support, and maybe a few boots on the ground. I don't know whether that would be enough for Biafra to win, though.