[Jeff Lee]

Slight tail light difference (you can convert the tail lights to 1968) and '67's lack side marker lights which were the small round lights in '68. For all practical purposes it's a toss up and I would claim it as a '68. There are far more obvious errors on year claimed. Apparently it's not the issue it once was.
You might want to look at the '67 383. If you have a fastback it's 10.67 class or SS/I with 300 factored HP. I know this engine can be killer in Stock and I reckon in SS also. The 1968 Fastback w/ 340 is 11.25 or SS/J @ 281 factored HP. Personally, I would rather run the 383. I think there is more potential there.
The '67 383 would be 3,170 with driver & the '68 340 would be 3,261 with driver in each natural class. You are now allowed to move both up or down (1) class from the natural class. So you could run SS/H along with me and weigh in at 3,020. Both of us can get squashed by those little 327 Nova's and 350 Camaro's!
Lastly, the killer - fast combo is now the '69 440 Barracuda rated at only 350 factored HP. That's a natural SS/G car and any of these combo's are acceptable with your 4-speed and Dana.