As I recall from installing a couple AFTERMARKET 4X4 fuel tank skids, there are four tabs that secure fuel tank straps to the cross members with four bolts. Two in front and two in the rear, squeezed up between the bumper area.
I have never pulled my fuel tank, but it would appear the easiest way to elevate the fuel tank two inches would be to either fab some spacers to achieve the lift OR fabricate new cross members piece that would safely support the fuel tank. I'd closely inspect the original mounts to ensure they aren't eaten up by rust before you attempt to modify them.
With the body elevated a few inches, you can at least explore your options, get some good measurements and fabricate the mounts off the truck for installation. If you are going to fabricate on the truck, then pull your fuel tank completely off your truck just to be safe. Even empty fuel tanks have an incredible kinetic force when they explode. Vapors are killers.