Body/chassis bolts should be M8 with a rectangular plate underneath and a washer on top, you should be able to get a socket up into the chassis channel to the nut without problems, I replaced all mine with stainless mushroom headed bolts that gives a smooth surface for the carpet. When done you can also take a grinder and cut back the body to the chassis and smooth it off, makes seats fit better and carpet smoother, surprising the difference 1/2" can make, she said.
helpful AND funny?! Peter you're the whole package!
Unfortunately, I don't see a way to get to the bottom of the bolts - there is no opening for me to get in unless I remove a number of bolts and that seems unlikely to be the only way. I'll provide some pictures when I get a chance tomorrow.
In the meantime, care to share what those mushroom head bolts you have look like?
Not quite sure what your plan is. The washers underneath are up inside the perimeter frame:
The bolts, as Peter mentions, are inserted from the top with their own washers:
In many cases, getting to those perimeter bolts is impossible without removing the side pods first, since the pods wrap the chassis at the bottom. If your pods are glassed in place.. you're SOL unless you cut the pods free.
If the bolts aren't loose or corroded, leave them alone. Since your pods are fiberglassed in, then yes, your are SOL if you wanted to replace them. You could trim back the sides from underneath to expose the rails, then do your thing, but better to leave well enough alone. If you were doing a body-off restoration, that would be an entirely different story.