You have to be very careful when trying to gasket match factory Magnum cast iron heads to any gasket. The pushrod punch is close to the intake port opening and the metal is fairly thin at the top of the port. If you try grinding too much you will go right through to the pushrod side.
I am not sure how much is really gained in this type of gasket match anyway, since the pushrod pinch is right there. It makes the larger intake manifold port open up further just to abruptly neck down again in the head at that pinch.
If it were me, I would make sure the intake port opening is not bigger than head opening, so there is not a wall the air hits, and then spend my time in the bowl area where the real gains are on a Magnum head.
