Sounds like a very nice victory! Congratulations!
I didn't make many changes to Kal-El's basic map. It has plenty of rubber in Malaysia and Indonesia, and I have now added oil on Borneo and Sumatra. A southern expansion should thus pay off in the long run.
The Samurai (iron) actually upgrades to Guard Infantry (saltpeter) - a new unit that comes with Constitutional Monarchy. This is in turn upgrades to Guerilla. The latter requires no resources, and acts as a cut off, making sure that no earlier units will be built. Another such cut off unit is the Rifleman. These two units both have two branches upgrading to them. Otherwise, all units along a branch have different resource requirements. This is especially important in the modern era. You would have seen it had you continued a few more turns. There you have the following land units to choose from:
Guerilla -> Heavy Infantry (rubber) -> Mech Infantry (rubber, oil)
Rifleman -> Infantry (rubber) -> TOW Infantry (aluminum)
Paratrooper (rubber) -> Modern Paratrooper (aluminum)
Naval Infantry (saltpeter) -> Marine (rubber) -> Special Forces (rubber, aluminum)
Attack Helicopter (oil, aluminum)
[Japanese] Tank (oil, rubber) -> Modern Armor (rubber, oil, aluminum)
Naval Infantry is an early Marine that comes with Navigation. You should always be able to build something! In earlier times there is, of course, even more variety - especially for Japan. But the role of the Samurai actually has changed considerably. It is no longer a cavalry unit. Instead, it is the Japanes version of the Knight - the Nakamaro Horseman - that upgrades to Japanese Cavalry. But the Samurai has some other nice features.

The equivalent of Medieval Infantry is, however, another type of Samurai. This has the following upgrade path:
Minamoto Samurai (iron) -> Musket Infantry (saltpeter) -> Guerilla
The spearman and archer branches are the ones that end up as riflemen. The predecessors of the paratrooper line are warrior monks, spies, and ninjas. The details are in the civilopedia!
I will update the files again to include the extra oil. And I look forward to hearing about your experiences in the next game!