I have a '67 chevelle that is powered by a 396 engine. This car originally came with a 6 cyl. eng. The car tilts to one side. The height diff. at the body bushings just below and to the front of the doors are almost 1".
I am trying to figure out if the frame is bent. Are there any ways to measure parts of the frame to determine this. Any help is GREATLY appreciated!

I think you have to "X" the frame. Measure from the center of the mount in front of the drivers door across and back to the mount in front of the passenger rear wheel well and the vice versa. I am no body man but my car sat crooked on the frame just as yours and my body guy said this is what they checked.
My body had to be removed from the frame and stretched. What was once a simple fix ballooned into a 3 year restoration, and I'm still not finished.