most of the time it is on the driver's side just bellow the injection pump. The numbers are cast onto the block and are about 1 inch tall. They aren't the little guys in a long string, it will just be the two of them.
They are also extremely rare to find in an 01, and they stopped using the block in 01.5, if you have rear disc brakes, you won't have a 53 block. in an 01 you should have a 55 or 56 block, or if you're lucky you have the mexican block.
Also, just to add this in, I have heard of people finding the block code in other places on the engine, but it really isn't that common. And the cracking block isn't a terribly common problem either. I heard a figure somewhere that fewer than 1 in 100 53 blocks crack. However, I can't back that up.
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