it depends on f350 vs f250. I belive the front coils are the same height but the rear blocks are 1-1.5" bigger on an f350 than the f250, long story short, i put the 2.5" on my f350 and it still sat a little stink-bugged. (*** high.) I would guess that the f250's are close to perfect. My procomp comp kit also came with a 1/2 rubber spacer ring to make the 2.5", the spacers were only 2" by themselves.
ps, my 2" metal coil spacer kit is up for sale if any one needs one. I dont have the 1/2 spacer though. pm me