For '68, one never truely knows what the car was w/o the orginal drive train... My car has everything required to be an SS except for one sticker. But no original drive train. So, was it an SS? I'd like to think so. Though, it is only an educated guess...
One other thing to check for that I can think of off the top of my head is fuel line(s). Then again, all these parts could have been swapped in from a donor car. The best advice I've seen it to verify as much as possible. Then, you are free to believe it to be correct. If you ever decide to sell it, you will have to be open to the fact that people will question it. That's just the way it is today...
It looks like your car needs some major work. Good luck on your project! It should be a lot of fun!