Other key points, use weld thru primer on all welds, drilling holes in the flanges on the weld side. I would also recommend AMD panels as they are the best fit. With AMD, make sure to buy all brackets and items that will fit the new metal part. It is not worth it to clean, straighten, sandblast and weld on the old ones. Get a good set of seam breakers. A plasma cutter if you are doing floors.
I mention AMD but if you are doing a Challenger, Dynacorn parts are a definite alternative. The fit is great and they come with most of the brackets, etc already put together. Saves lots of time. Unfortunately, Dynacorn only does Challenger although the parts on the front are almost the same including main floors, inner fenders, etc.
