Transmission casting/stamping identification

Any help would be appreciated in identifying this trans.  I believe it is not original to my 69 camaro, but from a 1970 vehicle.  The following are all numbers from the case:
 
3857577
B185303
3831707
3851325
P0728
3857584GM
 
Thanks in advance for any help.

Try here. http://www.nastyz28.com/chevy-transmission-identification.php
 
or here.  http://www.camaros.org/index.shtml