The door shells themselves are the same between notchback, fastback and convertibles, between their respective years. Convertibles DO have an external hard plastic SHIM that would be screwed in to match the anti-rattle mechanism found in the convertibles door jambs.
While the 1967 and 1968 model year door skins look VERY similar, there ARE MINOR differences.
1) The 67 (drivers) mirror is typically placed forward more closer to in the center or the vent window. The 68's are moved back slightly closer
towards the rear post of the vent window. The passenger mirror (if so equipped) would line up with is partner on the other side depending on the
year.
2) The 67 has an outward facing screw head holding the rear frame of the vent window in the door frame, whereas the 68's have a recessed screw
head with a little plastic filler over the hole. This filler is color coded to the upper frame paint color to be less conspicuous.
The 1969 model year mandated moving the interior door unlock pull knob forward approximately 8 inches towards the front of the car. The lower door vents were also removed.