The height of the rocker towers has no effect on lift. Because the head was milled 2mm the push rods are now 2mm to long. Because of this you would have to back the adjuster screws out to far to get the lash correct. So the choices are shorter push rods or raise the rockers 2mm. A friend made up some shims several years back when I had a different cam fitted, he also milled one set of rocker towers down .75mm. All this was done so that the valve geometry would have a wide range of adjustability. This way it was possible to get the proper geometry as well as getting the wear pattern centered on the valve stem. Getting the two is not always possible.