Patching floor and putting some new body bushings on 87

[chevymotocross]

I am going to have to replace the passenger side front cab bushing, as well as the rear cab passenger side bushing. The truck always had an awful creaking noise at the passenger floor. There is actually a big rotted hole there, and the cab bushing is basically doing nothing, since it's just a hole in the floor. The back passenger side cab bushing is ok, it's just missing the bottom donut and shim. I know how to weld, but someone told me this is a two-piece floor or something? I don't understand this maybe someone can walk me through? Here is a pic of what I'm dealing with.