If you go to the MPC TEXT PG 324 (SECT 95), you will come across the CARB APPL LISTING.

On application-

55 A (PASS CAR) (182HP SPL w F/M) 272
55 S (BIRD) w F/M 292
STAMPING ID NO - ECJ 9510-M - ECK 9510-T
Both ID NOS go to SVC PN B5A 9510-R and that carb shows no replacing/superseding PN.

ECJ 9510-M and ECK-T both showing going directly to SVC PN B5A 9510-R (PG 321 ID Crossover Chart)

What you have is a much later SVC REPL Carb. Was there an original parts box?

This is drawn from the 49/59 MPC FINAL ISSUE 1964. If you can find an earlier catalog or O.S.I. Manual, you may discover more info.

TED's HOLLEY CATALOG will most likely give more info.

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While the B5A-9510-R carburetor is not the original oem equipped carb for a 1955 Thunderbird, it did became a legitimate replacement to be used on the ’55 Thunderbirds when looking at the 1949-1959 Ford Car Parts catalog.  While it’s not concurs correct, there’s still some documentation showing it to be a viable replacement on the 1955 Thunderbirds.  There were several ’55 Thunderbird 4V carbs that became consolidated or replaced as the B5A-9510-R carburetor in that 1959 catalog.  Regardless of all that, Frank’s carburetor is a new carb and as such, would be a great replacement for any ’55 Ford needing a year correct model 4000 Holley. 
 
Depending upon how long any of those model 4000 Holley carbs has set on a shelf and what the storage conditions were, the rubber O rings for the fuel transfer tubes could be hard and brittle and potentially need replacing.
  

Lorena, Texas (South of Waco)