as stated the steel dash frame is different. (as are lower dash pads)
each year b-body frame 1968, '69, '70 is different as are frames for A/C cars. (if you are concerned with using the '68 pads, ignition switch, bits & pieces)

you need a '68 "rallye dash" frame from a Charger & Super Bee (STANDARD) or Coronet R/T (OPTIONAL)