Hi, I get a Olds 1957 2 doors, and I need to know where is the engine number, I read some threads about, and for that year suposed to be on the left side, between the spark plugs, but there is nothing.
Any other clue? here are some pics of the engine.

 

To verify its a 371 the number cast into the back of the block near the firewall would be the one. I can see it but not read it in one of your photos. A six digit number under the letters CFD. The heads being #16 would be correct for a 1957 371 engine. There's a stamp on a head above the #16 that I believe will key out if its a 2 bbl or 4 bbl engine originally. More details than that will have to come from one of the guys who knows more about this vintage than I do!

 

Here's an application number stamped on a head. This is off a 1959.

 

Seems you have to remove something to access the number?

 

It should be just below the valve cover lip. It will be on a smooth milled pad. If you don't see that check the other side head. If the engine has been worked on someone may have swapped the right and left side heads. John

 

#14 heads came on 1957. #16 heads were on a 1958.
The valve covers look to be repainted, so I think someone had the heads off too, since they are #16. Make sure the heads are both #16. Since the heads have been removed at some point, check the passenger side head for stamped numbers.

 

The engine number on 49 thru 58 Olds is stamped on the deck surface of the block.
It is just outside the head'
It can be seen by looking between the head and the exhaust manifold on the left side between cylinders 1 and 3.
You may need to scrape some dirt away with a screwdriver.