On all the late model trucks I've restored that I've replaced the rear floor in (almost all of em), even with rust similar to yours, I was able to transfer the fuel tank and heat shield brackets to the new floor. You can drill em loose with a spot weld cutter. Take careful measurements, and of course pay very close attention to left, right, front, and back before welding. You won't find a floor with all the brackets. Even the gas tank brackets can be duplicated if necessary with a little practice.
