Sedans are divided into two basic groups that are separated by the tail light size.
The better looking one , in my view, was the earlier, shorter one.
Heres the breakdown.
Smaller tail light with dome blinker = '67... 2 doors only. [4 door not invented yet.]
Smaller tail light with short spear = '68... 2 & 4 door.

Wide tail light with short spear = '69... 2 & 4 door.
Wide tail light with long spear = '70... 2 & 4 door.

In my view, the '68 had the best grille & the 4 door was the better looking of the sedans, so be proud of your car. They are great little movers. My 4 door is a '68 model & it has served me well for over 2 decades, but will now be "converted to components" & the 1200GX & 5 speed box from it will go into my 1000 coupe.
Chris
P.S. The serial number range for the '68 4 door sedan is from B10 - 80003 [from Oct. '67] to B10 - 200,000 [to Sept. '68]