The XS indicates the Charger R/T. The only engine options for the XS model in 68 would be the Hemi, engine code 73, or the 440, engine code 83.

If the engine code was 41, indicating a 318 engine, then the first two letters would be XP.

If this was an original XP car, indicating the standard Charger, then it was not an original Hemi car.