How good was the PRC's intelligence service? I was under the impression that they were a pretty third-rate bunch mostly operating in expatriate Chinese communities, and only badly there. Of course that could just be what Western writers believed. But I don't think there was much of a chance outside of areas with strong Chinese communities unless much more money and manpower was expended. That leaves - pretty much Southeast Asia. The Chinese already control North Korea, and a takeover of Mongolia, South Korea, Japan or Taiwan is pretty much illusory. I do believe they were pretty influential in Cambodia, Laos, Nepal and Indonesia at some point. The Philippines might make a good POD. I don't see Singapore or Malaysia falling to the Maoists.
Did Brunei have a sizeable expat Chinese population? That might give the West a good hard shock, what with all the oil gone.
Or could anyonbe envision a stronger Chinese involvement among the Euro-Maoist movement? I don't think their intelligence could hae handled the volatile political culture of Europe's wooly left fringe in the 60s and 70s (not to mention the USSR might take exception at their presence), but such contacts could be very valuable for destabilisation purposes.