Drilling Magnum heads for LA intake pattern

How does this index accurately to the head?
Using dye scribe a line dead center of bolt hole, the template is marked for that. At the bottom of template I have a stop to lay against the intake face bottom edge. If head has been milked then a shin of same thickness taken off can be added or just ream the intake hole bigger. I used vise grips to hold template yo head. A lot more to this process to make it work.

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