That sounds like a cool project. the first thing you need to find out is how much current the motors use. The Hero was fairly large so I would assume the Serializers H-bridges cannot handle the motors. that leaves 2 options, purchase new H-bridges, or use the existing ones. If the existing ones can take a PWM and Direction signal then you can control them directly from the serializer. If they need something else you will have to get a circuit to translate PWM+Dir to whatever it needs. If the hero has wheel encoders make sure they will work at 5V. Everything these days does, but I'm not sure what they used then.

Ringo