This block was on ebay recently and after recieving it I feel confident that the stamp is legit... the block is a 618 casting dated april 7th 1969.
It came with a set of GM pop up pistons and full floating rods.
It is a 4 bolt main block and the center set of bolts (where windage tray studs would go) are not there. The broach marks are present and there are no signs of any rotary machining marks anywhere.
http://www.crossroadspaper.com/69_Z28_DZ_engine_10.04.06%20012Cropped.jpg

Forgot to add that there is no VIN derivative on the block ...anywhere.

Any opinions?

OK??

Where's JohnZ at??

John, come on in..

pdq67

Looks real to me. Did you check for VIN by the oil filter mount?

I have searched it with a magnifying glass down there... it is raw casting no grinding or monkeying.

Im no expert but that sure looks like the real deal to me as well.