I was working on my 69 elco at school the other day, I had it on the frame rake because it was off to the left about an inch. After my teacher and I pulled that out another teacher used my car as a demo for his damage estimit class. He said that my frame rails are arched! Because my door jam gap is wider at the top on both sides of the car, but the gap between the rocker and the bottom of the door is even all the way across. Is this possible? I know shes been hit in the right rear, but there is no real evidence of a straight rearend crash. I want to be sure my frame is as straight as can be when i replace the right rear quarter panel. Also does anyone know if I can find the specs for the frame?

Do you have any pix? It would make things much easer to answer if we could see what your talking about.
That said, Check for worn or blown out body mount bushings. That could cause the body to sag on the frame. If not then you need to check the frame.
1968 - 1972 Chevelle Frame Dimensions
http://www.chevellestuff.com/tech/68-72_frame_dimensions.jpg
You can right click on the pic and save it to your comp.