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I references a hole being off in post # 125. Not an 1/8, maybe 1/16 inch.
Also I drilled all of my holes dry with no cutting oil of any kind.
One thing you want to be careful of is when you get to the bottom of your hole in that your about to push through don't strong arm it you can pop cast iron off the head.
I drilled all of my bolt holes completely through. When the manifold is bolted on the bolts will plug the oil from seeping through there.