For what it’s worth, .1.ada and .2.ada were the file extensions that the Rational Ada compiler used for spec and body, and Grady was one of the founders of Rational. GNAT is happy to use them as well if you tell it those are the extensions you are using.
The original Rational compiler generally didn’t preserve the source code as text files. It represented everything in Diana files, and reconstructed the textual representation of the source on demand.