5.56 and 7.62x39 Bren 2's only differ in barrel assembly, bolt assembly, gas cylinder, and the presence or absence of a magazine well insert.
Either factory folding stock will work on a 5.56 or 7.62x39 Bren 2. If I'm not mistaken, they will also fit on the 7.62x51 Bren 2 as well.