Jerry,
If they are both still 1958 rocker arm assemblies (never been swapped around over the past 51 years), then they should be the same.
Compare the following parts, to make sure everything is the the same size/length (try not to get the parts mixed up, just in case they are different):
- lifter height
- push rod length
- angles on the rocker arms
Also, you might want to check the face/surface on the rocker-arms where they push down on the top of the valve stems. If that surface is worn (dished), you might want to grind flat that surface on the rocker arms and polish that surface. This will give you a more accurate valve lash adjustment.
Tim
