When I have been at Corvette Auctions and a desirable Car is on the Block I have seen the Vette Dealers looking at the Casting Date on the Block and not being to concerned about the Serial Number. Before any of these Cars were of Collector Value it was consider'd Standard Engine Rebuilding to Resurface the Block durring a Rebuild. Restamping a Block is so common place now that the Casting date Probably means more today than it ever did. If You had a Car that You wanted to restore to matching Numbers You might spend Considerable Time and Money to Find a Block with close to the right Date but once You had it it would be Easy to have it Stamped. So if Your Checking Numbers on a Block Check the Serial Number, then the Date,and if these work togeather then the Broach Marks. The Broach Marks are the Hardest to Copy and the Hardest to Check, You must know what You are looking at. Hope this Helps. Richard...

Here's a nice shot of a factory STAMP PAD, where you can clearly see the "broach" marks. They are definitely hard to duplicate. What you are looking for are the straight lines running front to rear on the pad. The big blocks had broach marks that are a lot deeper, and therefore easier to see. These are the marks left by the broach machine in the above post pic.