All A + B body '67 bucket seats have the holes for headrests...just need the install kit, which I believe Classic still sells, and the correct year headrests...they go right in.
If they’re for a “Hi-Po” (Commando or Charger) 273, then they’ll be 65-67, which were only solid lifter ones, and will be the ball/ cup style pushrods, and will all be the same length.