All the '67-72 A-body 2dr's I've had interchanged on the front doors but the rears were different on some models. Some are different length and the window crank can be in a different spot. Some have arm rests and some don't and the mounting holes can be off a bit too. Do you need to have genuine '68 panels? Is yours a 100, 200, Signet? Do you care about color? Do you need all 4 or just the front? If you need just the front, can you post a photo of what your rears look like?
Thanks, Mark