Production numbers

can any body tell me how to tell the year of an engine by the number on the block?the number is3970020.thanks

Any idea on brand, type, size, year, displacement, etc?

That would make it too easy.

the eng is a chevy 350

That sounds like a ‘casting number’ and not an ‘engine number’. This site says it’s a 307 cid block, made from '69 to '73. http://www.mortec.com/castnum.htm

You’ll need the engine number to know more. See http://www.aacncclub.com/CHEVY_CASTING_NUMBER_LOCATIONS.html
for where to find it, and what it means.