Sooo, turns out I don't know when to stop. Probably some form of OCD sitting there undiagnosed ...
The trunk floor had been replaced already but there was quite a bit of porosity showing through in the plug welds that where apparently holding it down. I started to gouge some of them out so I could re-weld them. The more I poked, the more I came to the conclusion that I just wasn't happy with what had been done. The majority of the plug welds across the two rear chassis rails weren't actually tied in. In places there was up to a quarter inch of air gap between the trunk floor and the rail it was meant to be welded to. Also explains some of the warps that were in the trunk floor. So what started out as a tidy up a few few (dozen) welds, turned into me totally removing the trunk floor, drop sides, drivers side wheel tubs. Yes, the passenger side tub will come off as well, not happy there either.
So, very happy now that I have it sitting happily in the jig. I keep telling myself I'm getting closer to putting metal back into the rear of this girl ... at least I think I am
I've started cleaning up the freshly exposed rails, cross members etc. They will get a combination of weld through on the contact surfaces and 2k on all the rest before it goes back together.