Mike, I drilled mine in the manifold in the vertical part, just above the turbo. Drilled a small pilot hole and then the finish hole. The iron is soft.
I taped over the exhaust 3/4 with duct tape and drilled the holes with the engine idling. I shut if off before I tapped it, but filled the tap with grease to catch the cuttings.
No problems at all.
Good luck,
Blake