Going to do some further inspection on the carb next week. On the outside, it looks pretty low miles... but I haven't dug in deep yet.

For now I likely will use it, then do something else later if it seems prudent.

When I decided to use 2 of the Holley 2 barrel carbs I’d raced that never had been on a street engine and add one with choke housings I found we could never get the engine to a repeat idle. With starter fluid and a WD40 plastic tube I found all 3 shafts leaked excessively on both sides. With a bushing kit and inner nylon wraps I was able to seal them.
 I write this because older used carbs base plates if aluminum do wear and it’s hard to get some correct. I’m sure the rear barrels of vacuum secondary card will probably be good but it’s something to check when using older ones. 

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

Always keep in mind that the cfm rating of a carburetor is not the only determination for selecting a carburetor.  While the original 1957 Holley (List #1273) is rated at 410 cfm and the replacement Holley for the 1957 Thunderbirds (List #1848) is rated at 465 cfm, the replacement carburetor exhibits better low end torque and drivability aspects than the original due to improved metering aspects.  While he peak horsepower is the same for each, the torque is much better with the replacement carburetor.  Torque is what you feel when just driving the car around.

That’s a lead-in now for the larger carburetors and especially the Summit series or line of carburetors which is a modern revision of the older Ford ‘flat top’ carbs.  Besides the internal circuitry having the advantage of sixty plus years of improvements, the fuel discharge nozzles have also seen a redesign and improvement.  The Summit carbs have annular discharge nozzles for the fuel versus the ‘straight leg’ nozzles you find in the original and replacement Holley’s.  The annular discharge nozzles do a much better job of atomizing the fuel droplets as they enter the venturis versus what is observed on the straight leg and drop leg nozzles.  With that improved atomization you get an increase in fuel efficiency or fuel burn which translates into more power also.  The torque numbers also go up accordingly.

Also keep in mind that a vacuum secondary carburetor is only running on the primary side in normal driving.  With even a 750 cfm sized carburetor, it’s only utilizing half of that until the secondaries start to open.  The secondary side opens only as demand in the primary side dictates that so if the engine does not need all the available cfm, the secondary side only opens the amount required.  While a double pumper carb is very rarely sized exactly for an engines’ demands due to rpm and/or varying climate conditions, an oversized vacuum secondary carburetor will always be spot on in regard to what the engine wants regardless of the rpm and/or varying climate conditions.

Just some early morning ramblings so don’t let this be the end all for this discussion.

Lorena, Texas (South of Waco)

Napa, I sent a PM. I hope it helps.

A regular on this forum with a 55 Bird and what I would consider a build that is a good level above stock running a 390cfm Holley has always had praise for that carb. I think it's FloridaPhil.

64F100 57FAIRLANE500

Depending on the condition of your carburetor, it might/might not be rebuildable. Someone like Sal might be able to "tweak" it so that it will perform better than new, if it can be rebuilt.  

CORRECTION! According to Ted, the 57 carburetor is 410 cfm, not 465. He would know better than I. 

Awesome, thanks!! Again!

For only 45CFM difference in max flow from a new 500CFM carb, I definitely am more interested in using the vintage carb. 

The 55-56 Holley 4000 "Teapot" flows 390 cfm. The 57 4150 (1st year for same) flows approximately 465 cfm. Although the 57 carburetor is a 4150, it more closely resembles the 4160 carburetors. The replacement Holleys that the Tbird suppliers sell is a 4160 that has the same cfm rating. The new 4150 carburetors are dual-feed/w fuel lines on the passenger side. The 4160, like the 57 carburetor, is a single-feed on the driver's side. 

So, I am going with the general recommendation to use the factory '57 T-Bird carb. Does anyone have ideas as to it's flow potential? It's a 4150, that's the best I can find. The internet hasn't provided an answer, I am just curious. ECZ-AD List 1273-1 

Cool. Thanks for all the input. I appreciate it, all the time I spent professionally working on modern vehicles didn't much increase my know how about this stuff. Plenty to learn!