John 65

I have a 69 with a block cast as GM 41 3970010 I believe its a 1978 block (J 78) and it has the smaller front pad, which is blank. The dipstick is on the drivers side. No made in Mexico script either in the back. Did all the 010 blocks have the GM 41 prior to it? Not sure what I have here or what that means. Thanks

Easy Mike

The 010 block could be correct for a late build '69.

The casting date for the block should be in the web on the left rear corner of the block.

Engine code stamped on the pad will tell you when it was assembled and the vehicle it was originally meant to be installed in.

GD70

GM 41 I believe is the casting mold number

FrankVincent

The '41' on your block is called "pattern serial number 41".
The foundry poured 2 castings per cask (in this case, it would have been series 21, patterns 41-42).
Reason is that GM engineering was constantly making refinements to every block. If successful, the blocks were approved for the line. If not, they were destroyed. The first two castings would have been referred to as a COPE pattern, and instead of a normal date code tag, they would have received the "M" code specials tag. (Some books claim the "M" date code is a mis-stamp for the month of December)

I guess you can also refer to it as a mold number, but the mold in this case would be #21.
(Probably more than you ever wanted to know about this subject .. this information from the Saginaw Foundry Supervisor, Feb 2005)