How to check frame for straight

[walker]

I got my '67 home from the body shop where I had it towed after the wreck. Still not fixed but at least she is home. I was out surveying the damage today and I think she is savable. The d/s front quarter is wiped out pretty bad though. The sheet metal and grill are goners but the engine cab and doors are almost untouched. The spindle and lower a-arm are badly damaged. Before I get too far into this I would like to check out my frame for damage. There is some minor damaged to the front frame horns where the bumper bolts on but it doesn't look too hard to repair. I was wondering what the procedure is for checking the rest of the frame out. I watched the frame guys do this many years ago on an s-10 and thought that it could not be too much different than that. They some small plumb bobs that they hung from several locations on the frame and sighted down them and measured corner to corner. What locations should I use to sight/measure, and how far off is acceptable?