Take off the pads and get an idea how much difference it makes with the nut fit. A baseline. Maybe there is something else wrong. Did you put pads under the tank AND under the straps? If you did both it will shorten the straps. Looks like pads lay flat on the two tank supports. Just one pad thickness. None on the straps. Maybe study the FAM a little more.
The generic pads are for 49-72, so you don't use them all on every truck. You will need to "stretch" and pull the straps, especially if they have been bent during handling. Just moose it until the nut starts. Flatten and re-curve the straps to proper original shape. No kinks, no bends. Use a clamp, vice grip, channel locks to squeeze the taps together to get the nut on.
Tank must be in cradle and straps must be in depressions.
