It would be easier to help if you could please post pictures of the two head gaskets.  Currently, I can only offer a few general suggestions.  With the head gasket cooling water passage holes, you’ll want to make sure that the differences with the 7hp gasket won’t restrict the water flow any more than the 6hp gasket and that the water will still go through all the same passages in the motor.

When reinstalling the cylinder head, gently snug up one screw, then next the one directly opposite to it, then a screw next to the first screw, then the opposite screw to that last one and continue working in this pattern all the way around the cylinder head. Then, incrementally tighten up the bolts (using the same pattern) to the torque specification for your cylinder head bolts.  By using this method to tighten the bolts, you won’t warp the cylinder head.