When you remove the rusty bits of floor pan and you find that there is a rather large part of the car missing which contains most of the structural parts of the car it is best to have the car properly supported
There are two issues when you remove the sills from a car the first is panel fit and the second is suspension geometry, the car needs to both look and drive right. to keep the chassis straight we use the original rear axle locating points as the mounting point for our jig. We have put some studding through both the axle supports and then attaches this using substantial metal brackets to a steel sub frame
Then at the front we have carefully checked the condition of the two front chassis rails and we have decided that the cross member that is just behind the engine is a suitable position to attach the steel sub frame to. using substantial metal brackets we have now fixed the sub frame to the front chassis rails
Next you need to make sure that the body does not flex where the doors are mounted, to do this we weld two bars in the door aperture. For this we use some substantial studding and we do this before we remove the doors. You can use a special clamp to do this job but there is always a chance that it may slip and then you have reasonably serious issues to sort out.