From: http://forum.studebakerdriversclub.com/showthread.php?85607-V8-guys-let-s-talk-about-rocker-arms-adjusters-shafts-and-pushrods - Dec 2014 V8 guys - let's talk about rocker arms, adjusters, shafts and pushrods After fifty years, we're still learning about the Studebaker V8. This discussion arose because I just pulled down a '57 Packard version of the V8 which had been CASO'd with a mix of rocker arms. Some of us were trying to pin down how many variations of top end gear Studebaker V8s had over the years. Also, what can be swapped/combined and what shouldn't? I'm editing this as comments come in: 1. Rocker arms - three variations of the casting numbers I've seen. A. 536136 Early casting low drilled for oil to type A 7/16" hex screw B. 1550613 high drilled used type "B" 1/2"adj screw. C. High drilled type C 1/2" adj screw What years were the changes? 2. Adjusting screws - again, at least three variations. What years were the changeovers? A. 7/16" hex with machined radius in threading B. 1/2" hex straight thread and larger center hole C. 1/2" hex with machined radius in threading with small hole drilled transversely into the hollow body. (BTW - very bad juju to mix the wrong adjuster with the wrong rocker. Just because it will screw in doesn't mean it will oil correctly.) 3. Rocker shafts - two variations. Generally felt the '51-59 had a large oil feed hole and the 60-64 version had a smaller oil feed hole. Agree/disagree? Does this also correspond to the larger oil drainback hole in the head casting? 4. Pushrods - two lengths A. 11-3/16” or 11.171875 - 11.21875" B. 11-11/32” or 11.328125" - 11.375" Reference to year of the changeover? (Again, using the longer pushrod with the wrong rocker arm can require the adjuster to be screwed in so far it blocks the oil feed hole on some rockers.) Thanks in advance for the accumulated and shared wisdom of this forum. jack vines