I was fixing my leaking sun roof last weekend on my '87 and I removed the driver's seat in the process to inspect the floor. I had 3 of 4 seat studs snap off while trying to remove it. So I had to get out a plasma cutter and cut out the old mounts and fabricate new ones to be welded in. It really sucked and on top of that I still have a spot to fix around the right rear shock mount.

Ouch with out looking where ur located is this a northern car? The only thing OLD sunny had issues with where the perches for the rear lower springs were deteriated.I used a product called quick steel to fix the ball style mounts the rubber boots go over to fix this when I did my rear end resto work on mine.I guess being my car is from area nc rust is usually not a issue thank goodness.You seem to have alot of rust growing.Look at this way clean the area up and do some rust protection now bc new floor pans would be good but suck in terms of time,money in the long run.

Once I am sure the roof is repaired it will get new carpet and I will clean off the rest of the corosion. The right rear wheel well wouldn't have rusted around the shock mount if the previous owner hadn't under coated the wheel wells.