I was at the same point with my 68 Dart about 1.5 years ago, it was actually worse than that. I ended up making 2 cars into 1 as the 68 had good rails/rockers and I had a 67 with a good firewall/inner fenders and rear clip but the rails/rockers/floors were shot from sitting in the dirt.

After a month or so of planning I started bracing up the body and getting it square then started cutting and swapping, I had to haul it to a frame machine before I could hang the rear clip because the only thing holding the rear rails was what was left of the trunk gutter and the rails were pushed up about 3", the decklid was serving as part of the rear suspension since everything else was gone.

It was about the same deal up front, I swapped the firewall and inner fenders from the donor, and installed new pans front & rear, while I was at it I also seam welded all the factory spotwelds top & bottom, It's time consuming but I only had about $600 in parts for 4 new pans and the donor car.

At least if you go thru the whole car you will know there isn't and hidden rust or damage.