This is spit balling on drives to such a war but I'm very ignorant on both countries. Big question, what is the military capability of the two in this period?
Following 1967 both countries were pretty close to the United States. While minor operations maybe due to ships clashing say are possible, I doubt with Vietnam going on Washington would let two East Asian allies go at each other. Maybe post-Vietnam, Watergate period the US is both tired of Asia and focused on internal matters. Such a narrow window might encourage Indonesia to try a short war if it really desired too. But ultimately I think any major was will be fiercly opposed in Washington (not that a minor one would be greeted well).
Due to US connections to the Philippines and Indonesia being the aggressor I think its a very dangerous gamble for Suharto. The mid-1970s were his high point of control so he would have to be confident the Americans would no flip out totally. The mid 1970s in the Philippines were just as Marcos went from dodgy democrat to full blown dictator. There was also the Philippines First idea, basically claims on North Borneo, including Indonesian territory I think. If you have a South China Sea style build with the two nations standing off over small islands etc. - maybe Suharno declares he's protecting the people of Luzon and Sulu from the new tyranny (unlike his Directed Democracy of course) and uses a brushfire incident to launch a sudden attack.
However I'm predicting six months at most before threats and arbitration see the Americans end the war and then they'll only be minor territorial changes if any - Washington wouldn't want to reward either ally in order not to suggest to others the US will accept gains from such conflicts between its friends.