In the Heavy Gear universe the Gears are a mass manufactured stepping stone between infantry and tanks. Seems like they would be more applicable as the basic trainable soldier. Infantry would come in a couple of varieties (Anti-Infantry and Anti-Gear) and be quite cheap compared to the other forces. Tanks would probably work similarly to Sions (unalterable units available when a certain building is researched/produced).
Some heavy animation work would need to be done, as even though the Gears are humanoid, they have significantly different builds to humans. Plus I'm pretty sure the game doesn't have a "two handed rifle firing" animation.
The map making system would have to be altered so there was little/no water (most of the planet Heavy Gear is set on is desert, after all).
Don't get me wrong, I love the Heavy Gear universe and wish it had more attention. It just isn't an easy job to do.