Using the numerical body code doesn't work. It wasn't exclusive to A-bodies, a "23" code car was simply a hardtop. Challengers, Chargers, Satellites etc were all "23" model cars. An A body barracuda notchback is a "23" car too, that seat won't fit either. You can see a list of the body codes here, and note the amount of overlap. MyMopar - Mopar Forums & Information - 1967 - 1974 VIN Body Codes
The "LL" code isn't any better. A Dart could also be an LH or LM, that seat would work. So would a seat from a Scamp, that would be a VL, VH, or VM code.
The seat has to be from another 2-door hardtop Dart or Scamp. The earlier 2-door coupes (post cars) may work as well, but I haven't tried it.