Thanks for the kind words everybody.
I found a better picture of the finished tank install. I flipped and slid the rear crossmember back just enough to fit the tank. I also trimmed the bottoms of the frame rails a little bit, maybe a 1/2", to let the front of the tank fit. I just held the tank up the bottom of the frame with a floor jack and marked where to cut, and snuck up on it. I cut the hole for the fill neck with a big hole saw. Then I put the tank in position and bent a couple of flat bars to serve as the top supports for the tank.
I used a universal Speedway sender knowing I had to modify it. I ended up cutting it way down, but it seems to be working. You might be better off just buying a specific sender for this application though.
