This is a truck block.
Then a 3755011 348 block with the same deep eyebrow reliefs as the picture that Dick submitted, with a cast date of J460 would be a truck block even if there is no X on the front upper left side of engine? I think I may have been confused about the X being on all truck blocks.
Al 348 , passenger and truck, had the ex. relief notches. Some truck 348s had 2 relief notches. 409 passenger car blocks did not have the notches. Truck 409s do have the notches. Most 409s after 1962 had the X.
409's and 348's (962 and 655 castings) from CFD should have the X. What it comes down to, I believe, is that if it came with 333 heads, it should have one notch...:
Check the history out:
http://wiki.gmnext.com/wiki/index.php/Central_Foundry_Division
I learned that ArmaSteel was first developed in 1936 .
Cheers!
TomK