Installed the rear seat mounting hinges and the three floor stiffeners that are riveted with the hinges. I decided to forego Van's instructions in one area. They call for you to attach two holes in the right hinge to the left floorboard using LP4-3 pop rivets -- rivets that would have to be drilled out in order for the floorboards to come out. Instead (you guessed it), I installed nutplates and #8 screws through the those two holes in the hinge.
I did a test-fit of the floorboards with all the stiffeners finally riveted in place. It's just a little tighter and trickier to get the left-aft floorboard in and out, but it's perfectly do-able.
Installed the rear seatbelt anchors. Since I'm using Hooker harnesses that have steel bushings in the mounting ends, I had to modify the stock anchors by double-bending them a bit. This meant that there was not enough clearance from the aft side cabin covers, so I had to cut bigger slots in the cabin covers.
Every action has an equal and opposite reaction. If you try to build stuff fancy-like, you pay for it in lots of additional on-the-spot engineerin' and cipherin'. I think Pogo said that.