Engine dating

Hello,
I just bought an engine said to be a 1974 Corvette engine. It's an 010 block. It was almost given to me so I didn't ask any questions. Now I've taken it apart the block looks brand new, standard bore with hone-marks still visible, no measurable wear. Pistons are as new forged TRW L2256 with only very light wear marks. The Crank has definite but OK wear marks. This engine has definitely been rebuilt. So here's my question:
How can I tell the age of a Chevy Small Block casting?
Any help would be greatly appreciated, I'm somehow curious as to what I bought...
THX,
Max

There is a machined pad with numbers/letters right in front of the passenfer side head. Look up the last 2 or 3 letters here..........

http://www.nastyz28.com/chevy-engine-code-stampings.php

Post the number here and we can dechiffre it.
Or check at www.mortec.com

Kind regards from Cologne