First, I would suggest that Darmanitan will use Flare Blitz, as it gets boosted By Sheer Force, and I think that Charcoal is useless, either go with Choice Band, or Life Orb that gets boosted by Sheer Force.
Darmanitan@ Charcoal (Fire Punch)
(75)x(1.2)x(1.3)x(1.5)=175 BP
Darmanitan@Choice Band (Flare Blitz)
(140)x(1.5)x(1.5)x(1.3)=409 BP
Golurk@Spell Tag
(60)x(1.5)x(1.2)x(1.2)=129 BP
The Attack EV's you gave me would not help if the Pokemon you're battling against is unknown, so it's a useless information.