Trying to make it simple:

54-58 center groove rocker assemblies go on 54-58 heads.
59-62 offset groove rocker assemblies go on 59-62 heads.

If you want to use a 54-58 head on a 59-62 block your need a drilled head bolt.

http://chev235guy.blogspot.com/search/label/235%20Rocker%20Oiling
http://chev235guy.blogspot.com/search/label/235%20Drilled%20Head%20Bolt

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."