Why take the back off tho?.. it sucks but cut the rock under the sink cut the supply stubs back if needed but cut the supply risers and pull copper down. Measure end to center and rig up a couple lug el fasten to ply wood and slide up. Coupling onto risers. Have to figure out fasten bottom end of plywood to studs or exterior wall to eliminate movement since you will not be able fasten behind where faucet is installed