I was hoping to keep the doorstep panel in place, as im struggling to find a datum point to work from a everything has been patched so much.

If I remove them the only panel I have left to weld the floor to will be the bulkhead for now....all kind of chicken and the egg!
Im thinking of cutting a vertical section 10-15mm wide out of the inner A panel so I can bring the step panel in?
Would someone be able to measure the distance between the A panel lip at the top and bottom for me, so I can compare?