If you leave the top pad out then you're raising the car by the thickness of the pad and the U-bolt nuts will wind up further to take up the distance of the missing upper pad.
If you leave the bottom pad out then the U-bolt nuts will wind up further to take up the distance of the missing lower pad.
Regardless of whether you remove 1 or both pads, the U-bolt nuts will wind up further and you may run out of thread and you will need shorter U-bolts.
It's not uncommon to remove both top & bottom pads by competition cars in order to better locate the diff & eliminate the play which is inherent with having the pads in place. Escorts racers have been removing these pads for decades and using Anglia U-Bolts, which are shorter, to accommodate the missing pads. Other mods must be done if removing the pads, but a quick Google search will show you everything you need to know.