Engine decoding. What a pain...

[COBALT]

Last night I made my third attempt at finding codes on my engine (350-not original).

I found the casting number on back part of the driver's side behind the head (3970010, or something like that), which tells me it's a 2 or 4 bolt main 350 between '69 and '80. Yippie. I already knew that.

...but I haven't been able to find much else, and climbing around on top of the motor is getting old quick. I checked all along the block where the heads attach to see if anything is stamped in the block, but there's nothing there. I also looked behind the passenger side head and found a couple of casting symbols (an "S" I think), plus what may be a three number code but that's about it.

My goal here is to find out WHERE this engine came from. The more I work on it the bigger the mystery. Can anyone clue me in as to where information would be to help me solve this puzzle?