yea they need to be hooked together, but i not sure you'll get the flex you want like that, not without having a REALLY long travel shock
but on my truck that round crossmember is directly over the axle so my shocks are mounted there from the factory, but with the 2 inch body lift i could make a bracket to raise them another 6 inches to just under the bed floor
thats the plan that i had, when i put rear springs on ill let ya know how it goes.