http://1954advance-design.com/Stovebolt-engine/casting-numbers.html
http://www.gmpartswiki.com/getpage?pageid=213742
The head has a casted date code, where:
letter = month
number/number = day of the month
number = year
example L 15 7
December 15 1947

"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."