Driveline Hitting underside of floor (at rear)

Theres lots of really good suggestions here.
If the pinion angle turns out to be ok, and the front spring segment is ok and you really really don't want to change the stance, then I think you only have two options, which have already been mentioned;
1) swap out that Dana for a smaller rear, or
2) modify the floor.
Thing is; if you are running big power,or dragging it,the Dana could be justified(since its already in there).
And modding the floor on a convertible, may take some resale out of it.

So I vote to slip a smaller rear under there, with the correct pinion angle and a set of nice street springs, possible re-arched to set the stance. A bit of work, to be sure, but hey, winter is coming