I thought I would share what I have learned recently in trying to secure an original rebuilt carb off the interweb.  I have an original  Holley ECZ  AD, List 1273 carb on my '57 Tbird, that was in need of updating due to worn parts.  I found a nice-looking original one from a reputable rebuilder on eBay. It arrived with the incorrect metering blocks, air bleeds, no float bowl vent,  and would not run on the car. 
To add insult to injury, a nationally known rebuilder that lives nearby informed me that the eBay product had been re-stamped on the air horn, and was a forgery.   He said he had been seeing an increasing number of forged carbs on hard-to-find and valuable models, especially from vintage Corvettes.   I guess that practice has now entered the Thunderbird community.   
So, as they used to say on Hill Street Blues, be careful out there. 
 I will try to post some photos from a different appliance.   
Ralph 

Photos for above post.  Can you spot the forgery?

I’m guessing the top one is a forgery.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

How did the ebay seller respond?

You are correct the top one is bogus.  The seller has reimbursed me for the carb.
Ralph   

Has he stopped selling them? I don't know if it will do any good, but if he continues to sell them, and doesn't mention that they are not genuine Holley carburetors in the description, you should report it to ebay. 

Thanks for sharing about the counterfeit or forgeries of the ECZ carbs.  I was aware of this going on for the Corvettes and Ford performance carbs but this activity flowing over to the early Birds is a new one.  Here’s a picture of an original List 1273 Thunderbird carb and this particular one had the part number double stamped on the choke horn.  The date on this one converts to the first week of January 1957.
  

While this particular 1273 has the original body and metering blocks, the bowls were upgraded to the later model adjustable needle seat versions.  This List 1273-1 carb also has the newer vacuum secondary pot with the removable cover for quicker secondary spring changes and has been converted to a manual choke versus the original automatic choke.  There’s a lot of potential for changes in the 65 years since this particular carburetor hit the road.
  

Lorena, Texas (South of Waco)

I was amazed at the size of the air bleeds on the primary side of my original carb.  They were so large that I thought someone had drilled them out, or removed them entirely.  But I was mistaken.  After talking to the Holley Tech Line, who referred me to Daytona Parts Co. I learned that the stock bleeds in the 1273 were very large, and none even used on the high-speed bleed side (toward the center of carb). 
Ted, these large bleeds appear to be the ones in the carb you pictured.    
The forged carb had tiny air bleeds, but different than stock metering blocks (2015 main, 2547 secondary), which maybe were intended to run with the tiny air bleeds.  But, it would barely run on the car.  
Interesting times. 
Ralph