Here's a picture of the old support where the seat brackets bolt in. Just a reminder to make sure you cut those holes out. Did you notice how the "General" has his?
If you look at the arrows on this support and do a quick visual, this is kind of like you would be looking at the underside of a car to check it out. If you add the dirt and grime that's normally under there, you would think that the floors look okay. I have talked about this on different occasions and asked for pictures on another thread of floor pans and floor pan supports.
Here is a side view of the support above. I took a pair of pliers and spread it apart a little bit at the seam. You can see the rust popping loose and at the bottom of the picture you can see rust down in there.
This picture isn't any better, but that rust is at least 1/16" thick. I've found rust in some of these supports 3/16" deep. The reason I'm bringing this to your attention, is if you're thinking about buying a car, you really need a strong light, jackstands and good floor jack and get under there and look these cars over. We have southern cars and rust-belt cars. The rust-belt cars will have it packed in there like this as a rule, but the southern cars are also going to have some rust in there. Just wanted to point this out. A 40 year old car needs a good inspection. Just because the paint and the upholstry look good doesn't mean a lot.
There are a lot of burrs on here from the sheet metal screws so I ground them off.
This is what I used, a 2" roloc 36 grit disc.