Using Belly Drum will make it so that it doesn't matter if Charizard has higher special attack. A +6 boost makes it have very high attack. It also works well with Blaze and a Salac Berry. You'll want to go with Fire Punch, Thunderpunch, and Earthquake to back up Belly Drum. As for IVs, well, perfect IVs of course :P If you mean EVs go 252 Attack, 252 speed, 4 HP.