can anyone identify the numbers on this block?

I found this bare block and the guy told me it was a 413?? can anyone identify it?? the numbers on the side of the block are 7-21-61 & 1852029-4?
I have more info from the driver side front pad I don't understand? Its stamped KW006 and underneath that it stamped 040 so I'm thinking that might be bored out forty over???
One other strange thing some one has scribed 937EUAS SP on the pad and front of the block???? strange???
I posted this question on for Bbodies only but didnt get all the info so any help is appreciated!

It is a 413 and looks to be .040 o/s.. The rest I don't know. It might be in my Marine and Industrial book but I'm too lazy to look


http://www.rosevillemoparts.com/reference_castingnumbers1.php

http://www.440source.com/blocks.htm