Not sure if these will help or not,
Your driver side so you can orientate yourself....
The nut is welded to the little plate it's sitting on and that plate has a smaller square sitting at the very top which protrudes into the cab and rests flush with the floor from inside the cab.
This is the opposite side so you can see where it fits in the cab, but the welded nut and square fitting in the floor mean you just need to tighten the bolt, no need to grip it from underneath.
Not sure, maybe there's a factory plug or somewhere there you could knock out?
