As you can see I had to extensively modify the center trunk floor to allow space for the 15 gallon summit fuel cell. I was able to achieve 3 more inches by lowering the center trunk floor to the x-brace on the bottom of the rear frame rails. Luckily, I was able to reuse the existing floor pieces I had already installed, it just took some thinking and a lot of time. I don't have a sheet metal break, so I had to improvise by using blocks of wood, some straight pieces of flat stock and vise grips to get the bends I needed.
I needed to raise the driveshaft tunnel to go around the driveshaft loop, but didn't want to spend the money on a new tunnel from Chassisworks. I ended up using 2 leftover pieces from the wheel tub extensions that I bent over my leg to get the proper curve to attach to the loop. I made a straight relief cut about 2' long to lift the tunnel up to the extension I made. I think it looks good with the beads rolled in them, kind of like it was meant to be there.
The fuel cell is filled with foam, has a gm sending unit, and has -8 an fittings. I had to remove the fittings in the sump to install the cell in the trunk because it's such a tight fit.
I took JoshH's advise and bought the Quick Fuel 175 gph fuel pump. The bracket it came with wasn't going to work for my application, so I built a bracket/tray for it that also acts as a shield. It sits high enough that it cannot be seen from the back of the car. Still need to finish it.