I don't know about the gear ratio's but you could probably figure them out by finding out what number of teeth on each gear and going from there. CEN's website has nearly all the teeth numbers on their parts list/exploded diagrams.
I like the idea of the PC fan in there, does it help with the cooling in a significant way?? I've been toying with the idea of trying to stuff a skinny fan in between the rear shock tower and the engine. I don't really care about the extra weight of the fan and battery pack, the gen already weighs over 17lb what's an extra few ounces going to do

Buster