builing 8.5 brushless???

Was thinking about putting my hyper 8.5 back together for son and making it brushless. I was going to use the castle system 2200kv. With 2 7.4 5000. No brake servo, and what would you guys thik for a pinion for a good starting point. This will be my first electric 8 scale. And please dont recomend the novak system. Never again.. But any helpfull thoughts wouold be great or advice. THANKS