What to do with a floppy unibody?

Hi Guys,
I have started work on my next project which is a 1975 Australian Chrysler ute or 'truck' as you call them in your part of the world.
It is a unibody construction. Our 1970s Chrysler products have a lot of similarity body wise with what you produced in the States back then.
The problem I have is that the state of the body is worse than I thought it was ie it is floppy as the rockers are toast and there is less of a floor than I thought. The previous owner pop riveted a lot of panels in place, but that's another story.
Obvioulsy I need to 'stabilize' the body before I can start any restoration and was wondering what ideas you might have for this?
At this stage my plan is to run a couple of beams under the car from side to side and jack it up to try and level the car out as much as possible.
Thankfully the jacking points at the rear and front of the ute are solid enough to do this.
Once I have done this I will then have to work out some way to further align or tweak the body before finally welding in some steel to brace everything firmly. So that's my plan so far and I would really appreciate any ideas you may have. Has anyone had a similar situation before and how did you deal with it?
Appreciate any feedback.
Regards,
Ron
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