From "The Filling Station"
 

From today's email newsletter:

GMC Trivia
GMC Inline 6-cylinder engines had an easy way to tell the size (cubic inches) of their engines. How can you tell?
Look for the answer at the bottom of this newsletter

GMC Trivia Answer
Starting in 1939, most GMC six cylinder engines have the cubic inch size stamped in as the first three numbers of the stamped engine serial number. The number is stamped on the machined boss near the fuel pump.


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