As stated before, distributor in front for big blocks, like this:

If it's an RB block, like a 440, there is a flat, machined pad with the engine size, along with other codes, stamped on it just to the left (towards the drivers side) of the distributor, like on this '69 440HP block. Also notice how the deck sits about 1/2" above the as cast surface of where the water pump housing mounts:

On B blocks, like this 400 block, the pad doesn't exist. Also notice the same place on this block is machined flat:

Since B blocks have a shorter deck height, when the deck is machined, it gets cut all the way forward towards the water pump housing mount. That's why it's machined, and the pad on the passenger side is where the engine size, and other stuff, is stamped on these blocks.

If you can see it, the engine size is also cast at the end of the casting number on the left side of the block above where the starter would be. Here's the 400 block again:
