So they would basically be leading the world. Especially that if you add that a KMT China would have avoided Mao's starvations...they would probably have 1.5 or 1.6 billion of people, 2 if no one child policy. In any case, the population increase would have decreased naturally in the 70s-80s, like in all developed countries
I doubt that KMT China could go the export boom route post world war 2. The only reason why the US gave crazy market access to Japan, South Korea, and Taiwan was to counter Communist China. A KMT China will basically ruin any hope of Communist inroad into Asia. The US planned to have KMT China form an economic pendant with the rest of East and Southeast Asia. Expect more regional trade post war. The US will not give anybody in Asia market access right off the bat. It will have to be negotiated at GATT and opened up gradually.