I space the crossmembers down with blocks, on a 4" lift I use 3x4" blocks, on 6" I use 3x6" blocks, etc. to keep all the geometry the same as stock. I make strut towers for the front out of 4" pipe and 1/4" plate, in the back I bend and brace a piece of 1/4" plate to bolt the coilovers to.
