There's an Ad on Kijiji from someone looking for a B Manifold but He wants One that is correct  for 1957. Is there a casting # or any way to identify what Year these Manifolds were made for? I don't remember seeing anything like that on the One I have.

  

ECZ-B 4V intake manifolds were cast at least through the 1964 model year.  They were possibly cast after that as the engine blocks themselves were cast through 1967.  Mercury still used the 4V manifold in 1959 but went to a 2V carb on the 312 for the 1960 models.  After 1959, the ECZ-B manifolds were a truck item only.
 
Here’s the casting date location on a 1963 dated manifold.  This particular manifold has been modified to take the Teapot carburetor in conjuction with a Paxton blower.
 
On decoding the date, the first digit is the year, second digit is the month, and third/fourth digits is the day of the month.

Lorena, Texas (South of Waco)

 I have one that looks like a marine style blue so i'm wondering about boat usage. As land lubbers we forget about marine use. Thoughts? i'm assuming y's were in boats for a long time since the boat world is fine with solid lifters