Ideally, you want the plane of arc that the rocker sweeps to be coplanar with that of the angle of the valve stem.
To help visualize this: a line is defined by two non-coincident points. Think of the centerline of the valve as this line. The two points can be any two arbitrary points coincident with the centerline of the valve, defined by the center of the valve stem surface where the rocker sweeps and the other being the center of the valve seat.
A plane is defined by three non-colinear points, defined by the two previously mentioned points on the valve and the third point being the center of the rocker fulcrum. This is the plane that valve inclination lays in. The first picture illustrates this "Valve Plane." Note, the centerline to the right represents the centerline of the rocker arm stud.
The second plane is defined by the center of the rocker fulcrum and the center of the arc that the rocker roller sweeps (as installed). The second picture illustrates this "Rocker Plane" drawn with .030" offset between valve stem centerline and rocker roller centerline.
The further out of coplanar these two planes are: 1.) The greater the the misalignment at mid and peak lift. 2.) The greater the side-loading on both the valve and the rocker, as the roller tries to lift up on one side.
My remedy, when the trick adjustable guide plates are not available, is to cut the guide plates in half with a thin cut-off wheel in a die grinder; align each rocker by shifting its corresponding guide plate half, and then TIG weld the guide plate halves back together. I try to get the rocker as straight as possible throughout the range of lift.
Verify that there there is no contact between the push rod and the block or head throughout the lift range.
