Well, I dont know if your map is historical or a normal geo map...
I undertsand, and I think you are right, but no need to be 100% accurate. You will need change some borders. And I cant believe you are talking its difficult split some countries there...
But in fact, the truth is: the central region cant belong to 2 continents. You can call it "Central Indochina" or anything, but split it into 2 continents is impossible. How about the following continents: Central Indochina, North Laos (or another name), Tonkin (or Norht Vietnam), Cambodia, and South Vietnam (or Annam)? We can forget Cochinchina, or with some new countries we can maybe have 3 continents in the south side of the map
Sea ports? Are you serious? It will be worse, since we had already excess of borders...
Seriously, I know we can have 36 countries. And we need get free from the bottleneck. After that, the rest we can correct.