Stock Chevy 350 horsepower casting number 3970010?

That is the number of the block. It was used to build 302, 327, and 350 engines in 2 or 4 bolt main from 1969-1980.

There is a machined pad on the passenger side of the block just in front of the cylinder head that should have a combination of letters and numbers that can provide information about the horsepower and application.

Write down the numbers and look it up at this website: http://www.nastyz28.com/chevy-engine-code-stampings.php