As an amendment to the above, raising the rocker shaft will not correct the marching because of the racker arm contact to the valve stem. You would need longer valve stems that equal the shims you would have to add under the shaft. You cannot change the way the rocker hits the stem with out adding length, or removing length from the valves or push rods. Any change from the factory design will cause extreme stress on the guides and stems.
Its hard to explain, but I think if you mock up the head and block, you see it yourself after studying it a bit.
The number one concern is for the rocker to hit the stem in the center just before total lift or opening. For a full opening and closing the wear on a valve stem head should be equal distance from the center point of the stem. If its off to one side, the geometry is wrong.
Joe
