Pablo, I did find this info on the HAMB. (I DID a search, boy, the search police over there would LOVE me for that! )
Look for the engine number stamped on the block, top front right side just below the head. first two digits are model year, so if it's a 55 it will say 55xxxxxxx
thru 55 they are 331, 56-58 is 365, 59-60s 390
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the number in front of the head on the top of the block, passenger side, just like a Chevy V8