I'm looking at a '57 Super 88 that has triple carbs. Is there a way to tell if it's a real J2?

 

Unless you have the original sales invoice or a window sticker it's almost impossible to document a car as an original J-2.
There is nothing in the engine number, the VIN, or the fisher body tag that would tell you if it was a J-2.
Sixty five years on, it's very possible that J-2 components could have been added to 4 barrel cars.
The J-2 cars that are worth the most will have the original " bat wing " air cleaner and the correct numbered carbs and all the vacuum linkage.

 

my 57 is a J2 but my dad put the tri power on in 1959. It was a 4bbl car from the dealer new