Question about cab mounting hardware (shouldn't they be there?)

[goose_on_fire]

OK, hopefully this question doesn't reveal the depths of my ignorance...

I thought I'd pull up the seats & carpet to examine the floor and get a feel for whether I need to start searching for a new cab. Pulled up the passenger side, and noticed the bolt head was just sort of rattling around... so I just pulled it up and out!



I poked my head under the truck, and sure enough:



Nothing there (I've been driving it like that for who knows how long). So my natural thought is, "Hm, I wonder if the driver's side is also being held on due only to gravity (and the bolt being held down only due to the carpet)." Looked under the truck, and:



Sweet, got some hardware on this side! So I pull up the driver's side carpet and see this:



Shouldn't there be a bolt head there somewhere? Is there something I don't know? Did a previous owner have the audacity to just weld a new floor panel over the old one, cab mount and all?

From what I can tell from the chassis service manual, there should be a bolt accessible there. Am I wrong, or is it time to start cutting? Thanks!