What year block 26 GM 3970010 H312?

The block you referenced, GM 3970010 H312, indicates that it is a Chevrolet small-block engine produced in 1969. The "H" signifies that it was manufactured in August, and "312" indicates the 312th day of that month, which corresponds to August 31, 1969. This block is commonly found in various Chevrolet vehicles from that era, particularly in high-performance applications.