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If you look at the passenger side of the block,right at the distibuter you will find a similar string of numbers and yes from those numbers you will be able to get an idea of the year you have.

Also there is numbers on the distributer pad that will decifer the date built and plant of origin for your motor.

You can visit www.inliners.org site for all the listings.
According to that then I have a 55-57 261 in my 58 is that correct? 3837012<~block numbers from distributer plate.