Drilling magnum heads for LA intake

Despite the 6-Pack intake being no better than, and probably not as good as a say Air Gap intake, the visual impact is stunning and any power loss is minor for 99% of intended uses.
What I would do is carefully set the manifold on the engine and use a drill bit of exactly the hole diameter (may need numbered bits) to scribe a center point for the hole. Then take the head to a competent machine shop with a good drill press and level to drill the head and tap to the proper thread. It might be wise to even HeliCoil the head if you think you might remove the manifold frequenlty.