There are several different sites on the web to decode identification numbers. I don't remember what I used to find them for my 53 3100. Here is one site that might help <a href="http://www.stovebolt.com/casting.html" target="_blank">http://www.stovebolt.com/casting.html</a> and
<a href="http://clubs.hemmings.com/clubsites/chevytalk/GMhistory/index2.html" target="_blank">http://clubs.hemmings.com/clubsites/chevytalk/GMhistory/index2.html</a> Find the engine casting numbers (under the distributor) I think. Post any numbers you find on the block. Hope these sites help.