Go to the rctank website and look at Wil's #T017. The last 3 pictures will give you a idea of what tooth count you may want. You and I are using Will's #60 chain. So you need to figure out what tooth count you can use. His front gear is a 17x60. 17 tooth and #60 chain. He is using 5/8 bore size or 5/8 axle shaft diameter. And I can not find gears in anything other then 5/8 bore.
The IDLER gears you use for the non-driven axle. They have a bearing in center so they just idle. The DRIVE gears do not have a bore. You have to buy the X adapter to weld to gear. I have not found another sorce at this time. Remember #60 chain. That's the gears your looking for!