I think it depends a bit on what transmission you originally had in your car.
I have seen some part numbers that cover both 68 and 69, which would indicate to me that the head is the same in the instrument cluster. Quite often the differences are in the transmissions. If you had a 3 speed or a 4 speed in the car originally, I would test fit your existing one. If you went from an automatic to a 4 speed, I am thinking that you may need a 69 assembly.
Quite often the difference is in the length.
It can get kinda confusing. I think the advice of calling someone like NPD is good advice.