Just wait it gets worse, My Dad had a '73, 75, and '77. I have a '79. On all my Dad's he lost the rear floor pan and then as mentioned before came the rear leafs. Soon after a leaf or two would brake and he's dog track bad, then come the split on the roof where the corner of the window come, it has lead in there and I'm not sure why it seems to be so fragile. On the '77 we did get a "junk" car and cut out the floor pan... Dad didn't pay attention and cut just what he needed... no over lap to weld with. So if you do a replacement pan be sure that you allow for that. On my '71 Skylark we fabricated the pan. We found it very helpful to pop rivet the pieces in place and then we ran a bead weld. I also went a step further and used a clear caulking at each rivet and top and bottom of the pan.
Good Luck. I'm certain I'll be doing some of this to my Camaro this summer.