I'd say Focus Blast , I knoww low accuracy but you know once your defence is lowered infernape will easily be Ko'd .
Onother fact I noticed is most *not all , most , of the pokemon with the weakness of fighting have a higer defence than special defence cause most fighting moves are physical .
ex. Gigalith , Cloyster , RegiRock , Aggron , Onix , Steelix and many more.
So , go for focus blast holding an item that increases accuracy like Wide Lens .
Enjoy battling !! :)