I was surfing through the net when i came across this article in Wikipedia;
Chevrolet Big-Block engine
"Big block" is the term used to describe the large displacement V8 engines that were developed in the USA during the 1950's and 1960's. As American automobiles grew in size and weight following the Second World War the engines powering them had to keep pace. Chevrolet had introduced their popular small block V8 in 1955 but needed something larger to power their medium duty trucks and the heavier cars that were on the drawing board. The decision was made by Chevrolet to develop an all-new design for large-displacement use. This engine family had two generations, the "W" series, and the Mark IV series.
See link for more reading... really excellent!
http://en.wikipedia.org/wiki/Chevrolet_Big-Block_engineTheyres even reference to Rat Motors and Mouse Motors! ;41
M;36